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INTRODUCTION    TO    THE    STUDY 


OF 


INORGANIC    CHEMISTRY. 


BY 

WILLIAM   ALLEN   MILLER,    M.D. 

D.C.L.  LL.D. 

Late  Treasurer  and  Vice- President  of  the  Royal  Society  ;   Vice- President 

of  the  Chemical  Society ;  Professor  of  Chemistry  in  King's 

College,  London  ;  Fellow  of  the  University  of  London  ; 

Honorary  Fellow  of  King's  College. 


NEW  EDITION, 
WITH   QUESTIONS   FOR    EXAMINATION. 


D.     APPLETON      AND      CO. 

NEW    YORK. 

1881. 


P/SI 

PREFACE. 

_~_ 

THIS  BOOK  is  written  expressly  for  beginners.  In 
order  that  they  should  really  understand  the  state- 
ments which  it  contains,  it  will  be  necessary  for  them 
to  begin  at  the  beginning,  and  to  go  straight  through 
it.  Among  other  reasons  for  adopting  this  course,  it 
is  to  be  noted  that  it  is  impossible  to  avoid  the  use 
of  technical  terms  in  discussing  a  scientific  subject ; 
since  we  often  have  to  deal  with  matters  for  which  no 
expressions  are  in  use  in  ordinary  language.  In  this 
book,  when  a  technical  term  is  introduced  for  the 
first  time,  its  meaning  is  explained,  but  the  explana- 
tion is  not  afterwards  repeated.  Processes  are  also 
described  in  detail  when  first  mentioned,  but  when 
afterwards  referred  to,  they  are  simply  directed  to  be 
followed. 

Most  of  the  experiments  described  are  of  a  simple 
kind,  and  only  require  such  apparatus  and  materials 
as  may  be  easily  constructed  or  procured.  The 
student  is  strongly  advised  never  to  omit  the  per- 
formance of  any  experiment  which  he  has  the  means 
of  making.  No  useful  knowledge  of  Chemistry  can 
be  acquired  by  any  one  unless  he  constantly  makes 
experiments  as  he  proceeds  with  the  study. 

W.  A.  MILLE.R. 


NOTE. 

MY  FRIEND  Professor  MILLER  completed  this  work,  and 
placed  the  whole  of  the  MSS.,  including  the  Preface,  in  the 
hands  of  the  Printers.  He  was  actually  engaged  in  reading 
the  proof  sheets  up  to  the  time  of  his  visit  to  the  British 
Association  Meeting  at  Liverpool,  when  he  was  seized  with 
a  sudden  and  fatal  illness. 

Professor  Miller  placed  the  first  few  sheets  of  the  work  in 
my  hands,  and  requested  me  to  read  them  and  give  him  my 
opinion  as  to  the  mode  of  treatment.  I  accordingly  did  so, 
and  suggested  certain  changes  in  the  style  and  arrangement 
which,  if  adopted,  might  add  to  the  clearness  of  the  book 
and  so  far  assist  the  young  student  in  Chemistry.  He  ap- 
proved of  these  suggestions,  and  in  his  last  illness  left  a 
written  request  that  I  would  see  the  work  through  the  press. 
I  have  to  the  best  of  my  ability  complied  with  his  wishes. 

C.    TOMLINSON. 

HlGHGATE,  N. 

November  10,  1870. 


CONTENTS. 


CHAPTER   I. 

CHEMICAL  ELEMENTS— COMBINATION. 


PAGE 

1.  Scope  and  aim  of  Chemistry      i 

2.  Chemical    Elements  :     their 

mode  of  occurrence  .         .      4 

3.  Chemical  Notation       .        .      6 


4.  Weights  and  Measures         .  9 

5.  Physical  States  of  Matter      .  12 

6.  Mixture    distinguished  from 

Combination     .                 .  13 


CHAPTER   II. 

A.   THE  NON-METALS. 

ATMOSPHERIC  AIR — OXYGEN — NITROGEN. 


7.  The  Atmosphere  not  an  Ele- 

ment         .        .        .        .15 

8.  Oxygen         .         .         .        .19 
The    Pneumatic    Trough  — 

Collecting  Gases       .        .     20 

9.  Combustion .        .        .        .24 


10.  Measurement  of  Gases  under 

Standard  Conditions          .     28 

11.  Acids,  Bases,  and  Salts         .     30 

12.  Ozone 34 

13.  Nitrogen       .         .         .         .36 

14.  Air    a    Mixture    of    several 

Gases        .        .        .        .38 


CHAPTER  III. 

WATER — HYDROGEN. 


15.  Water  . 

Decomposition  of 
Freezing  and  boiling  of 
Evaporation 
Maximum  density 
Rain  Water . 
Spring  Water 
Hard  and  Soft  Water 
Tests  for 

Mineral  Waters    . 
Water  of  Crystallisation 


42 

45 
46 

47 
49 
50 
53 
53 
55 
57 


16.  Hydrogen  .  .  .  .58 
Collecting  Gases  by  displace- 
ment .  .  61 
The  Mixed  Gases  62 
Synthesis  of  Water  65 
The  Oxyhydrogen  Jet  67 
Diffusion  .  .  69 
Atomic  Weight  of  Hydrogen  70 
Hydrogen  the  Unit  .  .  70 
Monads,  Dyads,  Triads,  &c.  72 


vw 


Contents. 


CHAPTER  IV. 

OXIDES  OF  CARBON — CARBON. 


17.  Carbonic  Anhydride  .  .     73 
Sources  of    .        .  .  .78 
Ventilation    .         .  .  .79 
Synthesis  of  COa  ...     82 
CO3  in  the  Air  .  .83 

18.  Carbon         .        .  .  .84 
The  Diamond       .  .  .84 
Graphite       .         .  .  .85 
Pit  Coal  .     86 


PAGE 

Coke 87 

Charcoal  .  .  .  .88 
Animal  Charcoal— Filtration  90 
Allotropy  ...  92 

19.  Carbonic  Oxide    .        .  93 
Washing  of  Gases         .  96 

20.  Classification  of  Crystals  97 
Isomorphism         .        .            103 


CHAPTER   V. 
OXIDES  OF  NITROGEN— NITRIC  ACID— AMMONIA. 


21.  Nitric  Acid  ....  104 
22.  Other  Oxides  of  Nitrogen— 
Nitrous  Oxide  .         .         .no 
Nitric  Oxide          .         .         .112 
Nitrous  Anhydride        .        .113 

CHAP1 

Nitrogen  Peroxide 
23.  Ammonia 
Ammoniacal  Gas  . 
Absorption  of  by  Charcoal 
Solution  of  Ammonia   . 

^ER   VI. 

114 
114 

"5 
117 
118 

SEA  SALT  —  HYDROCHLORIC  ACID. 

24.  Chlorine 
25.  Hydrochloric  Acid 
Analysis  of   . 
Solution  of   . 
26.  Oxides  of  Chlorine 

.  120 
.  123 
.  125 
.  126 
.  129 

27.  Bromine        . 

.  132 

Hydriodic  Acid    . 
29.  Fluorine 
Hydrofluoric  Acid 

-  137 
.   138 
•  138 

CHAPTER    VII. 

SULPHUR  GROUP. 

30.  Sulphur        ....  141 
31.  Sulphurous  Anhydride  .         .  145 
32.  Sulphuric  Acid     .         .         .   147 
Nordhausen  Acid          .         .148 
Sulphuric  Acid  Chambers     .  149 
Salts  and  Tests     .        .        .151 

33.  Hyposulphites 
34.  Sulphuretted  Hydrogen 
Hydrosulphates    . 
35.  Carbon  Bisulphide 
Selenium  —  Tellurium    . 

•   152 

•   r53 
•   '55 
•  i57 
.  158 

CHAPTER  VIII. 

PHOSPHORUS  GROUP. 

36.  Phosphorus  . 
37.  Oxides  of  Phosphorus 

.  159   1          Sodic  Phosphates 
•  l63    1   37  a-  Phosphuretted  Hydrogen 

.  164 
.   1  66 

Contents. 


CHAPTER  IX. 

SILICON  AND   BORON. 


38.  Silicon . 

39.  Silicates  :  Glass 


PAGE 
.  168 
.  170 


39  a.  Boron 

Boracic  Anhydride 


PACK 
.  174 
•  175 


40. 


CHAPTER   X. 
COAL  GAS,  AND   OTHER  COMPOUNDS  OF   CARBON. 


Hydrocarbons 
Olefiant  Gas 
Marsh  Gas    . 
The  Safety  Lamp 
Flame  . 

Bunsen's  Burner  . 
The  Blowpipe 


177 
177 
179 
1 80 
181 
182 
183 


Coal  Gas      , 

41.  Cyanogen     . 

42.  The  Atomic  Theory 
Atomic  Weights    and 

mical  Equivalents 


Che- 


185 
188 
190 

193 


Atomic  Volumes  and  Mole- 
cular Volumes  .        .        .195 


CHAPTER  XI. 
B.    THE    METALS. 


43.  The  Metals  in  General .         .  198 
Specific  Gravities  and  Fusing 

Points  of  Metals        .         .  199 
Properties  of  the  Metals       .  200 


Metallic  Alloys     .        .        .201 

Native  Metals       .         .        .  202 

44.  Classification  of  the  Metals  .  202 


GROUP  I. — METALS  OF  THE  ALKALIES. 


15.  Potassium     .... 

Potash          .... 

Potassic  Chloride,  Carbon- 
ate, &c 

Nitre  or  Saltpetre 

Gunpowder  .... 
46.  Sodium  .... 

Common  Salt 


205 
206 


207 
208 
209 
210 
210 


47- 


Soda 210 

Sodic  Chloride,  Sulphate,  &c.  211 
Manufacture  of  Soda  .  .  212 
Tests  for  the  Alkali  Metals  in 

Combination  .  .  .  214 
Ammonium  ....  215 
Its  Carbonate  .  .  216 


GROUP  II. — METALS  OF  THE  ALKALINE  EARTHS. 


4.8.  Barium 
Baryta 

The  Sulphate 
Tests  for  Barium  Salts  . 
Strontium 
Calcium 


217 

—  */ 

2T7 

Mortar 

.    221 

218 

Calcic  Chloride    . 

.    221 

219 
219 

Gypsum 
Calcic  Carbonate  . 

.    221 
.    223 

210 

Tests    . 

.    323 

Contents. 


CHAPTER  XII. 
GROUP  III.— METALS  OF  THE  EARTHS. 


50,  Aluminum 
Alumina 
The  Alums 


PAGE 
.  223 
.  224 
.  226 


PACK 

Silicates  of  Alumina— Clays .  227 
Earthenware  and  China  .  228 
Tests  for  Aluminum  Salts  .  229 


GROUP  IV. — MAGNESIUM  METALS. 


51.  Magnesium  ....  229 

Magnesia      ....  230 

Magnesic  Chloride        .        .  230 

,,        Sulphate       .        .231 

Tests 231 


52.  Zinc 

Salts  of  Zinc 

Cadmium 

Indium 


232 
233 
234 
234 


53- 


54- 


CHAPTER  XIII. 
GROUP  V. — METALS  ALLIED  TO  IRON. 


Cobalt  .... 

Ferrous  Chloride, 
&c 

Carbonate, 

Nickel  .... 

.  236 

Uranium 

•  237 
.  237 

Tests  for  Iron       .        .        .  243 
55.  Chromium    ....  244 
Salts  of         ....  245 
Chrome  Yellow     .        .        .  246 
Manganese  ....  246 
Compounds  of  Manganese   .  247 
Tests    .                                  .  248 

Ores  of 
Manufacture  of  Iron     . 
Steel     .... 
Properties  of  Iron 
Oxides  .... 

•  237 
.  238 

•  239 

.  240 

Iron  and  Sulphur. 

.  242 

CHAPTER  XIV. 
GROUP  VI.— TIN  AND  ALLIED  METALS. 


56.  Tin 249 

Its  Alloys  ....  250 
Its  Oxides  ....  250 
Compounds  of  Tin  .  .251 


Tests 252 

Titanium,  Zirconium,  Thori- 
num,  Molybdenum  .  252 


CHAPTER  XV. 

I.   ARSENICUM.      2.   ANTIMONY.      3.   BISMUTH. 


57.  Arsenicum    ....  253 
Arsenic          .         .         ...  255 

Tests  for 255 

Arseniuretted  Hydrogen       .  257 


58.  Antimony     ....  258 
Compounds  of  Antimony      .  259 

59.  Bismuth        .         .         .         .  fc6o 
Compounds  of  Bismuth        .  2,61 


Contents. 


XI 


CHAPTER  XVI. 

I.   COPPER.      2.   LEAD.      3.   THALLIUM. 


60.  Copper 
Smelting  of  Copper 
Oxides 

Salts  and  Tests     . 

61.  Lead  . 


PAGE 
26l 
262 
263 
264 
265 


Action  of  Water  on  Lead 
Oxides  .... 
Salts     .... 
62.  Thallium 


PAGh 

.  266 
.  267 
.  268 
.  26q 


CHAPTER  XVII. 

THE    NOBLE    METALS. 


63. 

64. 
65. 

Mercury 
Its  Oxides     . 
Its  Chlorides 
Iodide  and  Tests 
Silver    . 
Its  Compounds 
Gold     . 

270 
272 
273 
274 
275 
276 
278 

Its  Chloride  .... 
Purple  of  Cassius  . 
66.  Platinum       .... 
Its  Chlorides 
Palladium,     Rhodium,     Os- 
mium, Iridium,  Ruthenium 

.  283 

279 
280 
280 
281 

282 

APPF.NDTX 

QUESTIONS    FOR    EXAMINATION  .        .  286 


INORGANIC    CHEMISTRY. 


CHAPTER  I. 

CHEMICAL   ELEMENTS — COMBINATION. 

(i)  Scope  and  aim  of  Chemistry. — Many  of  the  changes 
in  natural  objects  which  are  taking  place  around  us  every 
day — some  slowly,  some  quickly — are  the  result  of  a  class  of 
actions  which  are  called  chemical.  When,  for  instance,  a 
piece  of  iron  is  exposed  to  the  open  air  and  becomes 
covered  with  rust,  or  when  a  fallen  leaf  crumbles  away,  or 
when  milk  becomes  sour  after  it  has  been  kept  for  a  few 
days,  the  change  which  has  occurred  in  each  case  is  of  a 
chemical  nature  :  in  all  of  them  an  alteration  in  the  com- 
position of  the  substance  has  taken  place,  and  new  sub- 
stances, with  properties  quite  different  from  those  of  the 
original  material,  have  been  fornied.  The  iron  has  taken 
up  something  from  the  air  which  has  altered  its  colour  and 
lessened  its  strength;  the  leaf  has  furnished  new  bodies, 
some  of  which  have  passed  off  unseen  into  the  atmosphere; 
while  the  sugar  in  the  milk  has  become  changed  into  an 
acid,  and  the  curd  has  been  separated  from  the  whey. 

It  is  the  business  of  the  chemist  to  find  out  what  these 
various  substances  are  made  of,  as  well  as  the  exact  nature 
of  the  alteration  in  composition  which  has  occurred  in 
these  cases,  and  the  means  by  which  such  changes  can  be 

- 


2  Objects  of  Chemistry. 

forwarded  or  varied,  or  altogether  prevented.  Chemistry  is 
in  fact  the  science  which  teaches  us  the  composition  of 
bodies.  Whenever,  therefore,  a  new  substance  is  pat  into 
the  hands  of  the  chemist,  whether  it  be  derived  from  the 
mineral,  the  vegetable,  or  the  animal  creation,  one  of  his 
first  questions  is,  Of  what  is  this  body  made  ?  Is  it  com- 
posed of  one  kind  of  matter  or  of  several  kinds  ? 

In  order  to  obtain  answers  to  these  questions  we  must 
learn  to  observe  carefully  the  changes  which  are  going  on 
around  us;  and.  we  must  also  contrive  fresh  arrangements, 
more  or  less  altered,  in  which  the  exact  circumstances 
have  been  planned  by  ourselves  for  the  purpose  of  seeing 
what  will  happen  under  these  altered  conditions.  Such 
planned  observations  are  what  are  commonly  called  experi- 
ments-, and  the  better  they  are  planned  and  performed 
the  more  we  shall  be  able  to  learn  if  we  reason  accurately 
upon  the  result  obtained.  Chemistry  is  in  the  best  sense 
an  experimental  science,  calling  into  action  alternately  the 
head  to  plan,  the  hands  to  perform,  and  the  head  again  to 
explain  the  results  of  our  experiments. 

Various  substances  may  easily  be  shown  to  contain  more 
than  one  kind  of  matter ;  while  others  have  hitherto  foiled 
all  the  efforts  made  to  separate  from  them  any  second  sub- 
stance. For  example,  from  a  mass  of  pure  silver  nothing 
can  be  obtained  but  silver  itself,  copper  will  furnish 
nothing  but  copper,  and  from  sulphur  the  chemist  can  ex- 
tract nothing  but  sulphur.  Such  bodies  have  therefore  been 
called  undecomposed  or  simple  substances,  or  chemical  elements. 

On  the  other  hand,  such  bodies  as  table  salt,  iron  rust, 
water,  chalk,  wood,  mercuric  oxide,  may  each  by  the  use  of 
suitable  means  be  made  to  yield  more  than  one  kind  of 
matter. 

Experiment  I. — Place  a  scrap  of  wood  in  a  test-tube,  which 
is  a  glass  tube  about  the  size  of  the  forefinger,  and  closed  at  one 
end.  Heat  it  by  holding  it  just  above  the  flame  of  a  spirit 
lamp.  The  wood  will  become  charred  and  blackened  while 


Chemical  Elements- —  Combination.  3 

vapours  will  be  given  off,  and  will  collect  on  the  cold  sides  of  the 
glass  in  the  form  of  a  brownish  tarry  liquid. 

Exp.  2. — Place  in  a  test-tube  as  much  mercuric  oxide,  or  red 
oxide  of  mercury,  as  will  cover  a  sixpence,  and  heat  the  end 
of  the  tube  in  the  flame  of  a  spirit  lamp.  Oxygen  gas  will  come 
off  as  a  colourless  gas,  in  which  a  splinter  of  wood,  previously 
kindled  and  introduced  into  the  tube,,  will  burn  brilliantly,  and 
drops  of  metallic  mercury  will  collect  on  the  cold  sides  of  the 
tube. 

Such  bodies  as  wood  and  mercuric  oxide  are  said  to 
admit  of  being  decomposed,  that  is,  they  may  be  separated 
into  two  or  more  distinct  kinds  of  material ;  and  all  sub- 
stances which  thus  admit  of  being  analysed  or  pulled 
asunder  into  their  constituent  substances  are  known  chemi- 
cally as  compounds. 

In  many  cases  the  chemist  can  not  only  separate  a  com- 
pound into  its  elements,  but  he  can,  out  of  those  elements, 
by  synthesis,  or  putting  them  together  again,  build  up  the 
compound — as  may  easily  be  done  with  the  iron  rust, 
and  the  mercuric  oxide  just  mentioned.  When  a  body 
can  be  thus  separated  into  its  elements,  and  can  be  re- 
produced by  combining  those  elements  again  with  each 
other,  we  possess  the  most  complete  proof  of  its  chemical 
composition,  though  much  remains  to  be  discovered  respect- 
ing the  mode  in  which  the  different  substances  are  arranged 
in  the  compound.  We  may  know,  for  example,  what 
letters  are  wanted  to  spell  a  particular  word,  but  in  order  tc 
spell  the  word  correctly  we  must  also  know  the  order  in 
which  these  letters  are  to  follow  one  another.  Just  so  it  is 
necessary  to  discover  if  possible  the  arrangement  of  the 
elements  in  a  chemical  compound  before  we  can  be  said 
truly  to  know  its  constitution.  Every  material  object  with 
which  we  are  acquainted  is,  in  a  chemical  point  of  view, 
either  an  element  or  a  compound,  or  else  a  mechanical  mix- 
ture of  two  or  more  elements  or  compounds. 

By  far  the  greater  number  of  natural  objects  are  com- 

B  2 


4  Chemical  Elements — A  ttr action. 

pounds.  These  compounds  consist  of  two  or  more  simple 
substances  united  according  to  certain  fixed  rules  or  laws. 
The  simple  bodies  have  no  more  likeness  to  the  com- 
pounds which  they  form  than  the  separate  letters  of  the 
alphabet  have  to  the  words  which  may  be  made  from  them. 
The  power  which  causes  the  various  elements  to  unite  one 
with  another,  and  which  holds  them  together  after  they  have 
united,  is  called  chemical  attraction.  It  is  much  stronger 
between  some  elements  than  others,  and  is  exerted  accord- 
ing to  special  rules,  which  will  be  explained  hereafter. 

(2)  Chemical  Elements :  their  mode  of  occurrence. — Two  of 
the  most  important  of  the  elements,  oxygen  ana  nitrogen, 
form  the  principal  portion  of  the  atmosphere,  and  they 
occur  in  it  mixed  with  each  other,  but  not  chemically  com- 
bined. The  only  other  elements  of  importance  which  are 
met  with  in  their  separate  or  native  state  are  sulphur  or 
brimstone,  carbon  (in  the  very  different  forms  of  black-lead 
and  diamond),  iron,  copper,  bismuth,  mercury,  stiver,  gold, 
and  platinum;  but  some  of  these  are  found  much  more 
abundantly  in  combination  with  other  elements  than  in  the 
separate  form. 

The  chemical  elements  are  little  more  than  sixty  in 
number.  Most  of  them  occur  in  combination  in  the  strata 
of  the  earth.  Some,  indeed,  are  found  so  sparingly  that 
their  properties  have  been  but  little  examined.  Others 
again  are  extremely  abundant,  particularly  hydrogen,  oxygen, 
nitrogen,  and  carbon  ;  two  or  more  of  these  four  elements 
enter  into  the  formation  of  most  of  the  objects  familiar  to  us, 
except  the  ordinary  metals,  which  are  themselves  elementary 
bodies. 

Taking  the  earth  as  a  whole,  so  far  as  man  has  been  able 
to  penetrate  into  and  examine  it,  more  than  one-third  of  it 
has  been  found  to  consist  of  oxygen  either  combined  or  un- 
combined,  and  nearly  one-fourth  consists  of  silicon  in  com- 
bination, for  the  most  part,  with  oxygen.  Besides  this,  com- 
pounds of  aluminum,  calcium,  iron,  carbon,  magnesium, 


Chemical  Elements —  Metals —  Non-metals. 


5 


sodium,  potassium,  and  sulphur,  are  found  in  considerable 
proportion ;  some  confined  to  special  places,  and  the  others 
very  generally  diffused :  while,  dissolved  in  sea  water,  we 
have,  independently  of  the  oxygen  and  hydrogen  of  the  water, 
compounds  of  sodium,  chlorine,  magnesium,  calcium,  and 
potassium,  in-  addition  to  combinations  of  about  twenty 
other  elements  in  extremely  small  proportions. 

For  the  sake  of  convenience  the  elements  are  divided 
into  the  two  classes  of  metals  and  non-metals,  though  the 
two  classes  run  into  each  other.  Fifty  of  the  elements  are 
commonly  reckoned  as  metallic,  and  thirteen  as  non-metallic 
in  their  nature.  The  thirteen  elements  commonly  enume- 
rated as  non-metals  are  oxygen,  nitrogen,  hydrogen,  carbon, 
chlorine,  bromine,  iodine,  fluorine,  sulphur,  selenium,  phos- 
phorus, silicon,  and  boron. 

In  the  following  list  those  of  the  greatest  importance  are 
printed  in  capitals,  as  OXYGEN.  The  chemical  properties 
of  these  we  shall  examine  hereafter ;  those  in  ordinary  type, 
as  Bromine,  will  be  touched  upon  less  fully;  whilst  of  those 
in  italics,  such  as  Tantalum,  owing  to  their  rarity,  and  the 
absence  of  any  important  application  of  them  in  the  arts, 
few  will  need  more  than  a  passing  mention. 

ELEMENTS  WITH  THEIR  SYMBOLS  AND  ATOMIC  WEIGHTS. 


Name 

Symbol 

Atomic 
Weight 

Name 

Symbol 

Atomic 
Weight 

ALUMINIUM. 

Al 

27*5 

CHLORINE    . 

Cl 

35*5 

Antimony  (Stibium) 

Sb 

122 

Chromium 

Cr 

52'5 

Arsenicum 

As 

75 

Cobalt 

Co 

59 

BARIUM 

Ba 

137 

COPPER  (Cuprum). 

Cu 

63-5 

Bismuth 

Bi 

2IO 

Didymium 

D 

96 

Boron    . 

B 

II 

Erbiiim 

E 

112 

Bromine 

Br 

80 

Fluorine 

F 

19 

Cadmium 

Cd 

112 

Glucinum 

G 

9*5 

C  cesium 

Cs 

133 

Gallium 

Ga 

CALCIUM 

Ca 

40 

Gold  (Aurum) 

Au 

196-6 

CARBON 

C 

12 

HYDROGEN  . 

H 

I 

Cerium 

Ce 

92 

6  List  of  Elements — Notation, 

ELEMENTS  WITH  THEIR  SYMBOLS  AND  ATOMIC  WEIGHTS — cont. 


Name 

Symbol 

Atomic 
Weight 

Name 

Symbol 

Atomic  ' 
Weight 

Indium 

In 

"3'4 

Rhodium        •         . 

Ro 

104 

Iodine  . 

I 

127 

Rubidium 

Rb 

85 

Iridium 

Ir 

197 

Ruthenium     . 

Ru 

104 

IRON  (Ferram) 

Fe 

56 

Selenium 

Se 

79'5 

Lanthanum   . 

La 

92 

SILICON 

Si 

2o 

LEAD  (Plumbum)  . 

Pb 

207 

SILVER  (Argentum) 

Ag 

108 

Lithium 

L 

7 

SODIUM  (Natrium) 

Na 

23 

MAGNESIUM  . 

Mg 

24 

Strontium 

Sr 

*7'5 

MANGANESE  . 

Mn 

55 

SULPHUR 

S 

32 

MERCURY    (Hy-  ) 
drargyrum)         \ 

Hg 

200 

Tantalum      .         . 
Tellurium 

Ta 
Te 

182 

129 

Molybdenum  . 

Mo 

96 

Thallium 

Tl 

204 

Nickel  . 

Ni 

59 

Thorinum 

Th 

n.5'7 

Niobium         . 

Nb 

94 

Tin  (Stannum) 

Sn 

118 

NITROGEN    . 

N 

H 

Titanium 

Ti 

50 

Osmium         . 

Os 

199 

Tungsten     (Wol-  | 

W 

184 

OXYGEN 

O 

16 

framium)    .        \ 

Palladium 

Pd 

106 

Uranium       . 

u 

120 

PHOSPHORUS 

P 

3i 

Vanadium 

V 

51 

Platinum 

Pt 

197 

Yttrium 

Y 

597 

POTASSIUM  (Ka-  ) 

ZINC     . 

Zn 

65 

lium)  .         .        ) 

39 

Zirconium 

Zr 

89 

(3)  Chemical  Notation. — In  the  foregoing  table  it  will  be 
seen  that  opposite  to  the  name  of  each  element  is  placed  its 
chemical  symbol,  which  consists  of  the  first  letter  of  its  Latin 
name.  Where  two  or  more  of  these  names  begin  with  the 
same  letter,  a  second  letter  is  added  to  distinguish  such 
symbols  from  each  other.  These  symbols  form  a  simple 
and  easy  kind  of  shorthand,  by  means  of  which  chemical 
changes  may  be  clearly  and  compactly  represented. 

It  is  important  to  remark  that  whenever  the  symbol  of 
any  element  is  used,  it  represents  not  merely  the  element 
itself,  but  a  definite  quantity  of  that  element.  For  instance, 
the  symbol  O  always  stands  for  16  parts  by  weight  of 
oxygen ;  the  symbol  H  always  stands  for  i  part  by  weight 
of  hydrogen ;  and  in  the  table  opposite  to  the  symbol  of 


Chemical  Symbols — Notation.  7 

each  element  is  placed  the  number  of  parts  of  the  element 
which  that  symbol  represents.  To  render  our  ideas  precise, 
we  will  suppose  that  H  stands  for  i  gram  of  hydrogen  ;* 
then  O  will  represent,  not  I  gram,  but  16  grams  of  oxygen ; 
C  will  represent  12  grams  of  carbon;  S  32  grams  of  sul- 
phur, and  so  on.  The  reason  why  these  particular  numbers 
are  appropriated  in  the  table  to  their  corresponding  elements 
will  be  explained  hereafter.  They  constitute  a  very  impor- 
tant series  of  constants,  which,  in  the  case  of  the  more 
important  elements,  it  will  be  found  highly  useful  to  commit 
to  memory.  These  numbers  represent  what  chemists  have 
termed  the  atomic  weights  of  the  elements.  Every  element 
is  supposed  to  be  made  up  of  excessively  small  particles  or 
atoms  exactly  of  the  same  size  and  weight  in  the  same 
body.  If  the  atom  of  hydrogen  be  supposed  to  weigh  i, 
the  number  opposite  to  each  element  in  the  table  represents 
the  weight  of  its  atom,  or  smallest  particle,  compared  with 
that  of  the  atom  of  hydrogen. 

Compound  bodies  may  also  be  represented  by  symbols ; 
and  the  proportion  as  well  as  the  nature  of  the  elements 
concerned  is  easily  expressed  by  writing  the  symbols  side  by 
side  :  HC1,  for  instance,  represents  hydrochloric  acid,  a 
compound  of  hydrogen  with  chlorine,  in  which  the  propor- 
tion of  i  gram  of  hydrogen  is  united  with  35*5  grams  of 
chlorine  ;  H2O  indicates  water,  a  compound  of  hydrogen 
with  oxygen,  the  figure  2  below  the  symbol  H  multiplies  the 
quantity  of  hydrogen  by  2,  and  represents  2  grams  of 
hydrogen  combined  with  16  grams  of  oxygen.  When  two  or 
more  chemical  symbols  are  thus  written  side  by  side,  they 
constitute  a  chemical  formula.  Whenever  the  sign  +  is 
placed  between  two  formulae,  it  is  employed  to  show  that 
the  two  bodies  have  been  mixed  with  each  other.  The 

*  Another  unit  of  weight  might  have  been  taken,  such,  for  instance,  as 
I  grain,  or  I  ounce,  or  I  pound;  then  O  would  stand  for  16  grains  of 
oxygen,  1 6  ounces  of  oxygen,  or  1 6  pounds  of  oxygen,  according  as  a  grain, 
an  ounce,  or  a  pound  of  hydrogen  was  the  unit  chosen  for  the  comparison. 


8  Chemical  Symbols. 

sign  =  does  not  indicate  identity  or  absolute  equality,  but 
is  usually  employed  in  the  sense  of  the  word  'yields;'  and 
when  it  connects  the  two  halves  of  a  chemical  equation,  it 
represents  that  if  the  compounds  which  stand  before  it  are 
mixed  with  each  other,  with  due  precaution,  a  chemical 
change  will  occur  which  may  be  represented  by  the  arrange- 
ment of  the  symbols  placed  after  the  sign  =.  For  instance, 
in  the  chemical  equation, 

CaCO3  +  2HC1     =     CaCl2  +  H2O  +  CO2, 

CaCO3  is  the  chemical  formula  for  calcic  carbonate,  of 
which  marble  is  one  of  the  many  forms ;  and  if  H  represents 
i  gram  of  hydrogen,  CaCO3  will  represent  100  grams  of 
marble,  since  Ca  stands  for  40  grams  of  calcium,  C  for  12 
grams  of  carbon,  O3  for  3  times  16  or  48  grams  of  oxygen, 
making  together  100  grams.  HC1  is  the  chemical  symbol 
for  hydrochloric  acid ;  and  since  H  means  i  gram  of  hy- 
drogen, Cl  35*5  grams  of  chlorine,  2HC1  will  mean  twice 
that  quantity,  or  73  grams  of  hydrochloric  acid.  As  soon 
as  the  hydrochloric  acid  is  poured  on  the  marble,  a  chemical 
change  occurs;  the  marble  is  dissolved,  and  an  efferves- 
cence* is  produced,  the  result  being  the  production  of 
calcic  chloride,  CaCl2,  containing  40  grams  of  calcium, 
twice  35*5  or  71  grams  of  chlorine,  making  together  in 
grams  of  calcic  chloride;  H2O,  18  grams  of  water,  con- 
taining 2  grams  of  hydrogen,  and  16  grams  of  oxygen  ; 
while  CO2  stands  for  44  grams  of  carbonic  anhydride 
(or  carbonic  acid),  containing  1 2  grams  of  carbon  with  twice 
1 6  or  32  grams  of  oxygen,  and  this  has  passed  off  as  a  gas, 
and  produced  the  effervescence. 

The  whole  may  be  represented  as  follows,  where  the 
figures  written  under  each  symbol  represent  the  number  of 
grams  of  each  element  or  combination  of  elements  : — 

*  A  body  is  said  to  effervesce  when  it  gives  off  gas  suddenly  with  an 
appearance  of  boiling. 


Weights  and  Measures.  9 

Calcic  Hydrochloric  Calcic  wat*r  Carbonic 

Carbonate  Acid  Chloride  Anhydride 

CaCO3      +      2HC1      =      CaCl2      +     H,O     +     CO, 
40+12  +  16x3    2(1+35-5)    40  +  35*5x2    1x2  +  16    12  +  16x2 

100  73  in  18  44 

~~I73~~  173 

Or  in  words:  Mix  100  grams  of  marble  with  a  solution  of 
73  grams  of  hydrochloric  acid :  it  will  yield  1 1 1  grams  of  calcic 
chloride,  18  grams  of  water,  and  44  of  carbonic  anhydride. 

Whenever  a  chemical  compound  is  formed,  the  same 
compound  is  always  found  to  contain  the  same  elements, 
united  in  fixed  and  invariable  proportions ;  100  parts  of 
marble  always  contain  40  of  calcium,  12  of  carbon,  and  48 
of  oxygen :  and  in  like  manner  18  parts,  whether  grams, 
pounds,  or  tons  of  water,  always  contain  2  parts  of  hydro 
gen  and  16  parts  of  oxygen,  be  they  grams,  pounds,  or  tons. 

(4)  Weights  and  Measures. — The  weights  and  measures 
used  in  this  work  are  those  of  the  metric  system,  which, 
on  account  of  their  simplicity  and  convenience,  are  now 
commonly  employed  by  men  of  science  throughout  the 
world.  This  uniformity  of  usage  does  away  with  the  waste 
of  time  formerly  incurred  in  converting  the  weights  and 
measures  of  one  country  into  those  of  their  neighbours. 
As,  however,  most  persons  in  this  kingdom  have  been  ac- 
customed from  infancy  to  a  different  system  in  the  trans- 
actions of  daily  life,  it  will  be  necessary  to  explain  the 
principles  of  the  metrical  system.  It  will  be  needful  to  bear 
in  mind  that  the  metre  or  unit  of  length  is  equal  to  39*37 
English  inches;  and  consequently  that  10  centimetres  re- 
present very  nearly  4  inches,  while  a  millimetre  is  almost 
exactly  -^th  of  an  inch.  The  subdivisions  of  the  metre  are 
marked  by  the  Latin  prefixes  deci,  ten,  centi,  a  hundred,  and 
milli,  a  thousand ;  so  that  the  tenth  of  a  metre  is  called  a 
decimetre,  the  hundredth  of  a  metre  a  centimetre,  and  the 
thousandth  of  a  metre  a  millimetre.  The  higher  multiples 
are  indicated  by  the  Greek  prefixes  deca,  ten,  hecto,  one 


10  Weights  and  Measures. 

hundred,  kilo,  one  thousand ;  but  the  prefix  kilo,  or  multiple 
by  one  thousand,  is  almost  the  only  one  used  in  practice. 
For  instance,  the  higher  multiple,  or  1000  metres,  is  called  a 
kilometre.  It  is  used  as  a  measure  of  distance  by  road,  and 
represents  about  1094  yards,  16  kilometres  being  equal  to 
nearly  10  English  miles.* 


Fig.  i. 


Each  side  of  this  square  measures 

I  Decimetre,  or 
10  Centimetres,  or 
loo  Millimetres,  or 
3-937  English  inches. 

A  litre  is  a  cubic  measure  of  I  decimetre  in  the  side,  or  a  cube 
each  side  of  which  has  the  dimensions  of  this  figure. 

When  full  of  water  at  4°  C.  a  litre  weighs  exactly  I  kilogram  or 
1000  grams,  and  is  equivalent  to  1000  cubic  centimetres ;  or  to 
6 1 '024  cubic  inches,  English. 

A  gram  is  the  weight  of  a  centimetre  cube  of  distilled  water;  at 
4°  C.  it  weighs  I5'432  grains. 


isq. 

Centim. 


4  inches. 


*  The  metre  is  a  bar  of  platinum  deposited  in  the  archives  of  France, 
and  when  made  it  was  believed  to  represent  exactly  the  ten-millionth  part 
of  a  quadrant  of  a  great  circle  encompassing  the  globe  of  the  earth  on 


Metric  System. 


The  measures  of  capacity  are  connected  with  those  of 
length  by  making  the  unit  of  capacity  in  this  series  a  cube 
of  one  decimetre,  or  3*937  English  inches,  in  the  side;  this, 
which  is  termed  a  litre,  is  equal  to  17637  imperial  pints,  or 
to  61-024  cubic  inches. 

Finally,  the  system  of  weights  is  connected  with  both  the 
preceding  systems  by  taking  as  its  unit  the  weight  of  a  cubic 
centimetre  of  distilled  water  at  4°  C. :  it  weighs  15*432 
English  grains.  The  gram,  as  this  quantity  is  called,  is 
further  subdivided  into  tenths  or  decigrams,  hundredths  or 
centigrams,  and  thousandths  or  milligrams,  the  milligram 
being  equal  to  about  -fa  of  a  grain. 

The  higher  multiple  of  1000  grams  constitutes  the  kilogram. 
It  is  the  commercial  unit  of  weight,  and  represents  15,432 
English  grains,  or  rather  less  than  2 \  Ib.  avoirdupois. 

The  weight  of  1000  kilograms,  or  a  cubic  metre,  of  water, 
is  0*9842  of  a  ton,  which  is  sufficiently  near  to  a  ton  weight 
to  allow  of  its  being  reckoned  as  one  ton  in  rough  calcu- 
lations. 

The  temperatures  given  in  this  book  are  expressed 
throughout  in  degrees  of  the  centigrade  thermometer,  unless 
otherwise  specified.  The  following  is  a  short  comparative 
table  of  the  two  scales,  Centigrade  and  Fahrenheit. 


c. 

F. 

C. 

F. 

C 

F. 

C 

F. 

-20° 

-4° 

15° 

59° 

45° 

113° 

75° 

167° 

~I5 

+  5 

20 

68 

5o 

122 

80 

176 

-10 

14 

25 

77 

55 

131 

85 

185 

-  5 

23 

30 

86 

60 

I40 

90 

194 

0 

32 

35 

95 

65 

149 

95 

203 

5 

41 

40 

104 

70 

I58 

IOO 

212 

10 

So 

the  meridian  of  Paris.  But  it  has  been  found  by  later  and  more  ac- 
curate measurements  that  this  assumption  is  erroneous.  The  metric 
system  is,  however,  no  way  dependent  upon  the  accuracy  of  this 
assumption,  and  the  actual  bar  of  platinum  then  made  continues  not- 
withstanding to  be  the  unit  of  the  metric  system. 


1 2  Solids — L  iquids —  Gases. 

(5)  Physical  States  of  Matter.— Most  of  the  simple  bodies 
of  the  chemist  occur  as  solids  at  the  common  temperature 
of  the  air ;  two  only,  mercury  and  bromine,  exist  as  liquids  ; 
while  four  others,  viz.  oxygen,  hydrogen,  nitrogen,  and 
chlorine,  are  known  as  gases  ;  but  in  one  or  other  of  these 
three  forms  of  solid,  liquid,  or  gaseous  every  substance  exists, 
whether  it  be  simple  or  compound. 

Solid  bodies,  such  as  a  bar  of  iron  or  a  block  of  wood, 
have  a  definite  form,  which  cannot  be  altered  without  the 
application  of  some  force  more  or  less  considerable. 

Liquids,  on  the  contrary,  like  water,  when  placed  in  an 
open  vessel  yield  to  the  slightest  force  :  their  particles  slide 
easily  over  each  other;  they  adapt  themselves  at  once  to 
any  un evennesses  of  the  bottom  or  sides  of  the  vessel,  and 
they  always  present  a  level  surface  in  an  open  vessel.  They 
do  not  become  smaller  by  compression  in  closed  vessels  to 
any  extent  which  can  be  seen  by  common  observation. 

Gases,  on  the  other  hand,  like  air,  yield  easily  to  com- 
pression. In  closed  vessels,  when  the  pressure  upon  them  is 
increased,  it  can  be  seen  that  they  are  forced  into  a  smaller 
space ;  and  when  the  pressure  is  lessened  the  space  filled  by 
the  gas  becomes  larger.  Hence  gases  are  sometimes  spoken 
of  as  elastic  fluids.  They  are  always  tending  to  increase  in 
bulk,  and  they  always  completely  fill  the  vessel  which  con- 
tains them,  no  matter  how  irregular  may  be  its  shape. 

Many  bodies  may  be  made  to  assume  either  of  these  three 
states  at  pleasure,  and  to  pass  slowly  backwards  and  for- 
wards from  one  condition  to  the  other  for  any  number  of 
times  by  simply  altering  the  temperature  to  which  they 
are  exposed.  Ice,  water,  and  steam,  for  example,  are  the 
same  chemical  substance  in  three  different  physical  states, 
and  the  same  quantity  of  water  may  be  raised  into  steam, 
and  converted  back  again  into  water  or  into  ice  as  often  as 
may  be  desired.  The  alteration  of  the  form  of  a  body  does 
not  affect  its  weight.  A  gram  of  ice  when  changed  into 
steam  still  weighs  a  gram  although  we  no  longer  see  it;  and 


Mixture — Chemical  Combination.  13 

every  litre  or  other  fixed  measure  of  each  has  a  definite 
weight,  as  may  be  easily  proved  by  the  use  of  proper  means. 

All  the  solid  elementary  bodies  except  carbon  have  been 
melted,  though  some  require  a  very  intense  temperature. 
Some  of  the  metals,  such  as  platinum  and  a  few  of  the  metals 
which  accompany  it  in  its  ores,  cannot  be  melted  in  ordinary 
furnaces ;  but  the  extreme  heat  of  the  voltaic  arc  or  the 
electric  current  produced  between  the  poles  of  the  voltaic 
battery  converts  all  the  metals  not  merely  into  liquids  but 
even  into  vapour,  and  at  this  exceedingly  intense  heat  all 
compounds  are  separated  into  their  elements.  On  the  other 
hand,  most  gases  may,  by  the  united  action  of  cold  and 
great  pressure,  be  reduced  to  the  liquid  state  ;  among  these 
are  chlorine,  sulphurous  anhydride,  carbonic  anhydride,  and 
hydrochloric  acid  ;  several  of  these  have  also  been  frozen  by 
intense  cold  into  masses  like  ice  or  snow.  A  few  gases, 
including  the  elements  oxygen,  hydrogen,  and  nitrogen,  have 
never  been  liquefied,  though  it  can  scarcely  be  doubted  that 
their  liquefaction,  and  even  freezing,  would  be  effected  could 
we  apply  a  still  more  intense  degree  of  cold  and  pressure 
combined. 

(6)  Mixture  distinguished  from  Combination. — When  once 
a  chemical  compound  has  been  formed  its  components  can- 
not, as  a  rule,  be  separated  by  merely  mechanical  methods. 
A  piece  of  marble,  as  we  have  seen  (p.  8),  consists  of  three 
elementary  bodies — carbon,  oxygen,  and  calcium.  It  is  easy 
to  grind  the  marble  to  a  powder  of  extreme  fineness,  but 
every  fragment  of  that  powder  is  still  marble,  and  no  one  by 
mere  grinding  could  separate  the  carbon,  the  oxygen,  and 
the  calcium  from  each  other.  The  molecule  or  minutest  par- 
ticle of  marble  which  can  exist  separately  is  still  a  compound 
substance  formed  of  still  smaller  particles  or  atoms,  of  the 
elements  carbon,  oxygen,  and  calcium.  To  accomplish  the 
separation  of  these  atoms,  which  together  form  the  molecule 
of  marble,  we  must  employ  some  new  power ;  and  one 
which  the  chemist  finds  his  most  useful  ally  in  such  cases  is 


14  Difference  between  Mixture 

heat.  If  the  marble  be  heated  for  a  time  to  bright  redness 
it  is  decomposed.  The  carbon  with  part  of  the  oxygen  is 
driven  off  as  a  compound  gas,  and  the  calcium  with  the 
rest  of  the  oxygen  remains  behind  in  the  form  of  the  solid 
compound,  lime.  Still,  by  this  means  a  partial  separation 
only  of  the  three  elements  has  been  effected,  two  new  com- 
pounds having  been  formed  instead  of  the  original  one. 

Again,  it  seldom  happens  that  by  mechanical  means  alone 
we  can  make  two  bodies  unite  chemically  with  each  other. 
In  making  gunpowder,  for  example,  which  is  a  mixture  of 
sulphur,  charcoal,  and  nitre,  the  three  substances  are  first 
ground  separately  to  a  fine  powder.  They  are  then  mingled 
together,  moistened  with  water,  and  ground  for  several 
hours  under  edge  stones,  in  order  to  mix  them  as  intimately 
as  possible :  after  this  they  are  subjected  to  intense  pres- 
sure, and  finally  broken  up  into  grains.  But,  notwith- 
standing all  this,  gunpowder  still  remains  only  a  mechanical 
mixture  of  its  three  components,  nitre,  charcoal,  and  sulphur. 
The  nitre  may  be  washed  out  of  the  mixture  by  means  of 
water ;  the  sulphur  may  be  dissolved  out  of  the  remainder 
by  means  of  carbon  disulphide,  and  the  charcoal  will  be  left. 
On  evaporating  the  water  the  nitre  may  be  recovered  un- 
altered; and  on  allowing  the  disulphide  to  volatilise  or 
escape  in  vapour,  the  sulphur  will  remain  behind.  But  the 
mixed  materials  are  ready  in  gunpowder  to  act  chemically 
upon  each  other;  for  if  a  spark  fall  upon  the  powder  a 
sudden  change  occurs,  a  flash  follows,  and  a  prompt  che- 
mical action  takes  place,  in  consequence  of  which  a  large 
volume  of  gas  is  produced,  while  the  heap  of  powder  is 
converted  into  new  substances,  several  of  which  are  gases, 
and  none  have  any  resemblance  to  the  original  materials. 

Mechanical  mixture,  then,  and  chemical  combination  are 
two  very  different  things  ;  they  ought  never  to  be  confounded 
with  each  other,  although  the  mistake  is  often  made  by 
beginners.  Whilst  in  every  true  chemical  compound  the 
proportion  of  its  constituents  is  perfectly  fixed,  in  a 


and  Chemical  Combination.  1 5 

mechanical  mixture  the  proportions  of  the  substances  of 
which  it  is  made  may  be  altered  to  any  extent  that  may  be 
desired;  besides  this,  the  mixture  always  preserves  proper- 
ties which  are  intermediate  between  those  of  its  compo- 
nents. A  mixture  of  table  salt  and  sugar,  for  instance,  may 
be  made  by  grinding  the  two  together,  and  the  quantity  of 
either  may  be  varied  at  pleasure.  Its  flavour  will  par- 
take of  the  saline  taste  of  the  one,  and  of  the  sweetness  of 
the  other;  the  degree  of  saltness  will  vary  according  as  the 
proportion  of  salt  to  the  sugar  is  increased  or  diminished. 
But  each  particle  of  salt  and  of  sugar,  however  small,  still 
continues  a  true  chemical  compound  unaffected  by  the 
other,  and  in  each  of  them  the  quantity  of  the  constituent 
elements  is  unchanged. 

Further,  in  the  case  of  every  true  chemical  compound,  not 
only  are  the  proportions  of  its  constituent  elements  fixed, 
but  the  properties  of  the  compound,  for  the  most  part, 
differ  totally  from  those  of  the  separate  elements  which  form 
it,  as  well  as  from  those  of  the  mixture  of  the  two  elements 
before  they  have  become  chemically  united.  The  truth  of 
this  we  shall  see  as  we  proceed,  and  the  first  case  in  which 
we  shall  have  occasion  to  observe  it  is  in  the  chemical  pro- 
perties of  the  air,  which  we  shall  now  examine. 


CHAPTER  II. 

A.    THE   NON-METALS. 

ATMOSPHERIC   AIR.      OXYGEN — NITROGEN. 

(7)  The  Atmosphere  not  an  Element. — We  are  surrounded 
on  all  sides  by  a  viewless  substance,  the  air,  which  though 
commonly  unnoticed,  makes  itself  felt  at  once  in  every 
gust  of  wind  which  blows.  Every  ' empty'  vessel,  as  it  is 
usually  called,  is  really  full  of  air. 


1 6  Atmospheric  Air. 

Exp.  3. — Take  a  glass  bottle  and  press  it  with  its  mouth 
downwards  into  a  basin  of  water.  The  water  will  not  fill  the 
bottle,  for  it  is  already  full  of  air.  Now  turn  the  mouth  of  the 
bottle  upwards,  still  keeping  it  under  water ;  bubbles  of  air  will 
escape,  and  when  all  the  air  has  thus  been  allowed  to  pass  out 
the  bottle  will  have  become  full  of  water. 

So  lately  as  a  hundred  years  ago  the  air  was  thought  to 
be  an  element ;  but  it  may  easily  be  shown  that  it  is  truly  a 
mixture  of  several  different  substances,  some  of  which  are 
simple  bodies,  and  others  are  chemical 
2-  compounds. 

Exp.  4. — Fasten  a '  short  bit  of  candle 
tofa  flat  piece  of  cork  (Fig.  2).  Float  it  on 
some  water  in  a  soup  plate;  light  the 
candle,  and  place  a  jar  full  of  air  with  its 
mouth  downwards  over  it.  In  a  few 
minutes  the  candle  will  burn  dimly,  and 
then  will  go  out. 

The  air  which  is  left  will  no  longer  allow  a  candle  to  burn 
in  it  j  it  has  become  altered  in  its  properties  by  the  burning 
of  the  candle,  and  has  experienced  an  important  chemical 
change.  Other  substances  besides  a  burning  candle  will 
produce  chemical  changes  in  the  air. 

Exp.  5. — Take  a  glass  jar  6  or  8  centim.  in  diameter  and 
25  cm.  high;  moisten  it  upon  the  inside,  and  sprinkle  over 
the  moistened  surface  a  thick  layer  of  iron  filings  ;  then  place  it, 
with  its  open  end  downwards,  over  water  in  a  soup  plate,  and 
set  it  aside  in  a  warm  room  for  a  day  or  two  :  the  iron  filings 
will  gradually  grow  rusty,  the  bulk  of  the  air  in  the  jar  will  be- 
come less,  and  the  water  will  rise  slowly  until  it  stands  about 
5  centim.  higher  in  the  jar  than  it  did  at  first ;  after  this  the 
bulk  of  the  enclosed  air  will  not  be  further  lessened.  If  a  flat 
plate  of  glass  be  now  slipped  under  the  open  end  of  the  jar, 
the  whole  may  be  lifted  out  of  the  water ;  and  on  placing  it 
mouth  upwards,  and  then  removing  the  glass  plate,  and  at  once 
putting  into  the  jar  a  lighted  taper  fastened  to  a  wire,  as  shown 
in  Fig.  3,  the  taper  will  immediately  cease  to  burn. 


Experiments  on  Air, 


Fig-  3- 


The  iron  in  rusting  has  taken  away  something  from  the 
air  which  enabled  the  taper  to  burn  in  it;  and  that  some- 
thing is  the  elementary  gas  called 
oxygen.  The  remainder  of  the  air 
in  which  the  taper  will  not  burn 
consists  chiefly  of  another  gaseous 
element,  called  nitrogen. 

The  candle  in  burning,  Exp.  4, 
also  took  oxygen  from  the  air,  and  it 
went  out  as  soon  as  it  had  taken  up 
a  certain  quantity  of  the  oxygen  con- 
tained in  the  air  enclosed  by  the  jar. 

Other  metals  besides  iron  may  be 
used  to  remove  oxygen  from  the  air, 
particularly  if  they  are  heated  with 
it.  If  mercury  be  used  for  the 
purpose,  it  will  not  only  remove 

the  oxygen,  bujt  it  may  be  afterwards  made  to  give  it  up  again 
in  a  separate  form. 

Exp.  6. — This  experiment  Fig.  4. 

requires  some  days  to  com- 
plete it,  but  it  is  very  in- 
structive, and  may  be  made 
in  the  following  manner  : — 
Into  a  dry  flask  provided 
with  a  neck  50  centim.  or 
more  in  length  introduce 
about  40  grams  of  clean 
mercury ;  then  bend  the 
neck  of  the  flask  twice 
upon  itself,  into  the  form 
shown  in  Fig.  4,  and  plunge 
the  bend  into  a  small  Wedg- 
wood-ware mortar,  contain- 
ing mercury,  so  as  to  leave 
the  open  end  of  the  neck 
projecting  above  the  surface  of  the  metal  into  a  jar  containing 

c 


1 8  Experiments  on  Air. 

air,  which  is  to  be  supported  over  it.  Now  apply  the  heat  of  a  lamp 
to  the  flask,  and  keep  the  mercury  for  two  or  three  days  at  a 
point  just  below  that  necessary  to  make  it  boil.  Red  scales  will 
be  formed  slowly  upon  the  surface  of  the  mercury  in  the  flask ; 
and  these  scales  after  a  time  will  no  longer  increase  in  quantity. 
If  the  lamp  be  then  withdrawn,  and  the  whole  allowed  to  cool, 
the  bulk  of  the  air  will  be  found  to  have  become  considerably 
less.  The  hot  mercury  has  acted  chemically  on  the  air  both 
of  the  flask  and  of  the  jar,  owing  to  the  free  passage  of  both 
portions  through  the  neck. 

The  gas  which  is  left  consists  almost  entirely  of  nitrogen. 
On  adding  mercury  till  the  height  outside  and  inside  the 
jar  is  the  same,  and  then  withdrawing  the  stopper  and  in- 
troducing a  lighted  taper,  supported  on  a  wire  handle,  it  will 
be  put  out.  A  mouse  or  other  small  animal  would  also  soon 
die  if  plunged  into  it.  The  oxygen  is  the  portion  of  the  air 
necessary  to  support  the  life  of  animals.  If  one  or  two 
grams  of  the  red  scales  formed  by  thus  heating  mercury  in 
air  be  placed  in  a  test  tube,  they  may  be  made  to  give  up 
the  oxygen  again  by  heating  them  still  more  strongly. 

Exp.  7. — Fit  a  good  cork  to  the  mouth  of  the  tube ;  then  with- 
draw the  cork,  and  with  a  round  file  bore  a  hole  through  it,  just 

large  enough  to 

FlS-  5-  admit  a  narrow 

glass  tube,  bent 
as  shown  in  Fig. 
5.  Heat  the 
tube  and  the  red 
scales  in  the 
flame  of  a  spirit 
lamp  while  the 
open  end  of  the  narrow  tube  is  dipped  under  water.  Bubbles  of 
gas  will  soon  begin  to  come  off.  Next  fill  two  or  three  narrow  jars 
or  wide  test  tubes  with  water ;  close  them  with  the  finger,  and  in- 
vert them  in  the  basin  ;  collect  the  bubbles  of  gas  in  one  of  them 
as  they  escape  from  the  narrow  tube.  The  first  jar  will  be  filled 
chiefly  with  the  air  originally  in  the  heated  tube ;  this  may  be 
thrown  away  ;  but  if  into  one  of  the  other  tubes,  when  filled  with 


Air  a  Mixture.  19 

the  gas,  a  splinter  of  wood  on  the  end  of  which  is  a  glowing 
spark  be  plunged,  the  wood  will  burst  into  a  flame. 

The  mercury  used  in  the  flask,  Fig.  4,  has  in  fact  sepa- 
rated the  atmospheric  air  into  two  portions,  one  of  which, 
the  nitrogen,  will  not  allow  a  candle  to  burn  in  it,  and  is 
left  unacted  upon  by  the  metal  ;  while  the  portion  which  is 
active  in  supporting  flame  has  combined  with  the  mercury, 
and  converted  it  into  the  red  scales.  When  these  scales 
are  heated  more  strongly,  they  become  separated  into 
metallic  mercury,  and  into  the  gas  which,  as  we  have  seen,  is 
highly  fitted  both  for  the  support  of  life  and  for  the  burning 
of  such  bodies  as  may  be  kindled  in  the  open  air.  This  gas 
is  called  oxygen  (the  '  acid  producer'),  because  it  forms  a 
needful  part  of  many  acid  bodies. 

A  fixed  weight  of  mercury  will  always  unite  with  a  fixed 
quantity  of  oxygen.  For  instance,  400  grams  of  mercury 
will  combine  with  exactly  3  2  grams  of  oxygen,  and  will  form 
432  grams  of  the  red  oxide.  If,  again,  432  grams  of  these 
red  scales  of  mercuric  oxide  be  decomposed  by  heat,  and 
proper  care  be  taken  to  collect  the  whole  of  what  is  given 
off,  400  grams  of  liquid  metallic  mercury  would  be  found, 
and  32  grams,  or  about  22*4  litres,  of  gaseous  oxygen. 
These  changes  may  be  represented  in  symbols  as  follows  ; 
the  quantities  of  each  substance  are  written  beneath  :  — 

Mercuric  Oxide  Mercury          Oxygen 

2Hg    O         =          2Hg       +       Oa 
2(2OO+l6)  2  X  2OO  l6  X  2 

(8)  OXYGEN:  Symbol,  O;  Atomic  Weight  ',  16;  Atomic 
Volume,  |  |;  Specific  Gravity,  1*10563;  Relative  Weight,  16;* 
Molecular  Weight,  O2,  32;  Molecular  Volume,  £  ^].  f 


Exp.  8.  —  There  are  other  means  of  obtaining  oxygen  :  one  of 
the  best  is  by  heating  potassic  chlorate  (KC1O3).     This  salt  may 

*  See  page  30. 

t  See  the  chapter  on  the  Atomic  Theory  for  an  explanation  of  these 
terms. 

C  2 


2O  Mode  of  Collecting  Gases. 

be  mixed  with  about  its  own  weight  of  black  manganese  oxide 
in  fine  powder.  This  oxide  should  be  first  made  red  hot  in  a 
covered  clay  crucible,  and  allowed  to  cool ;  it  should  then  be 
ground  up  in  a  clean  mortar  with  the  chlorate.  The  manganese 
oxide  enables  the  oxygen  to  pass  off  from  the  chlorate  at  a  much 
lower  heat  than  is  needed  if  the  salt  is  heated  alone,  although 
the  oxide  itself  undergoes  no  permanent  change.  30  or  40 
grams  of  this  mixture  may  be  put  into  a  clean  and  dry  Florence 
oil  flask,  provided  with  a  good  cork,  through  which  is  passed  a 
tolerably  wide  bent  glass  tube.  The  flask  is  to  be  placed  with 
the  end  of  the  tube  dipping  under  the  water  in  the  pneumatic 
trough.  Fig.  6.  If  the  mixture  in  the  flask  is  heated  over  a  lamp, 
gas  comes  off  freely,  and  may  be  collected  in  jars  placed  for  its 
reception. 

Fig.  6. 


A  pneumatic  trough  for  experiments  upon  gases  may  be 
easily  made  out  of  a  small  tub  or  pan,  which  is  to  be  nearly 
filled  with  water.  A  shelf  must  be  fixed  at  one  end,  so 
as  to  be  3  or  4  centim.  below  the  surface  of  the  water,  or 
the  glass  jar  may  even  be  supported  on  a  brick;  3  or  4 
jars,  each  holding  about  a  litre,  may  be  used  to  receive  the 
gas.  They  should  be  open  below,  and  one  or  two  may  be 
provided  with  a  glass  stopper  ground  to  fit  the  neck.  They 


Oxygen  Gas.  21 

may  be  filled  with  water  in  the  trough,  and  placed  with  the 
bottom  downwards  on  the  shelf.  As  they  become  filled  one 
after  another  with  the  gas,  they  can  be  removed  by  sliding  a 
plate  under  each,  while  the  mouth  is  still  under  water,  and 
then  lifting  the  plate  and  jar  together  out  of  the  trough. 

Though  the  potassic  chlorate  is  more  easily  decomposed 
when  mixed  with  manganese  oxide  than  when  heated  alone, 
the  pure  salt  may  be  made  to  give  off  oxygen  by  heating  it 
more  strongly  by  itself. 

Exp.  9.  —  Place  about  a  gram  of  the  salt  in  a  test  tube, 
and  heat  it  over  a  spirit  lamp;  The  chlorate  snaps  and 
flies  to  pieces,  or  decrepitates,  when  first  heated.  It  then 
melts  and  forms  a  clear  liquid,  which,  when  heated  more 
strongly,  gives  off  bubbles  of  pure  oxygen  gas.  The  mass  gra- 
dually becomes  white  and  opaque,  and  ceases  to  give  off  oxygen, 
leaving  a  white  residue,  consisting  of  chlorine  and  potassium 
only,  and  known  as  potassic  chloride.  The  gas  at  first  often 
looks  cloudy,  owing  to  little  particles  of  the  salt  which  are 
carried  over  suspended  in  it  in  fine  powder,  but  these  gradually 
become  dissolved  in  the  water. 

245  grams  of  the  chlorate  would  give  off  96  grams  of 
oxygen,  or  about  67-2  litres  of  the  gas.  The  change  may 
be  thus  represented  :  — 

Potassic  Chlorate  Potassic  Chloride 

2K    Cl     03          ~        2K    Cl      +       30, 
+  16x3)  2(39  +  35-5)          6  x  16 

245  H9  96 


If  the  mineral  known  as  black  manganese  oxide  (MnO2) 
be  made  red  hot,  oxygen  may  also  be  obtained  from  it  ;  but 
only  one-third  of  its  oxygen  is  thus  driven  off,  or  about  one- 
ninth  of  the  weight  of  the  mineral  if  pure.  The  ore  of 
manganese,  however,  always  contains  impurities,  which  cause 
the  oxygen  gas  to  be  mixed  with  more  or  less  of  other  gases. 
The  black  oxide  when  heated  becomes*  converted,  with  loss 


22  Oxygen — Mode  of  Preparing. 

of  oxygen,  into  a  reddish-brown  oxide  of  manganese:  261 
grams  of  pure  black  oxide  would  yield  32  grams  of  oxygen, 
or  2  2' 4  litres  of  gas. 

Black  Oxide  Red  Oxide  Oxygen 

3Mn      O2        =       Mn3        O4 

3(55  +  16x2)  55x3+16x4 

261  229 

"""261 

Exp.  10. — Procure  a  gaspipe  or  an  iron  tube  3  or  4  centim.  in 
diameter,  40  or  50  cm.  long,  closed  at  one  end,  and  provided  at 
the  other  with  a  cork,  through  which  is  passed  a  long  piece  of 
pewter  or  copper  tubing ;  place  50  or  100  grams  of  the  oxide  in 
small  lumps  in  the  tube,  and  make  the  closed  end  of  the  iron  tube 
red  hot  :  gas  will  be  driven  off,  and  may  be  collected  over  water. 

Red  lead,  nitre,  and  several  other  substances,  also  give  off 
oxygen,  more  or  less  pure,  when  heated  ;  but  either  potassic 
chlorate,  or  manganese  oxide,  or  the  mixture  of  both,  is  the 
substance  from  which  it  is  usually  and  most  easily  obtained. 

Oxygen  is  a  clear,  transparent,  colourless  gas,  which  has 
never  been  liquefied  by  cold  or  pressure ;  it  has  no  smell  or 
taste.  No  other  gas  can  be  used  instead  of  oxygen  for  the 
support  of  respiration  in  man  and  animals ;  but  it  cannot  be 
safely  breathed  in  a  pure  state  for  any  length  of  time,  as  it 
would  over-excite  the  bodily  frame.  The  nitrogen  with 
which  it  is  mixed  in  the  air  is  needed  to  dilute  it,  so  that 
it  may  be  respired  with  safety.  Oxygen  is  attracted  by  a 
magnet  like  iron. 

Oxygen  is  remarkable  for  its  great  chemical  activity.  It 
will  combine  with  each  of  the  elementary  bodies,  with  the 
single  exception  of  fluorine.  Substances  which  will  burn 
in  air  burn  in  oxygen  with  much  greater  energy,  as  may  be 
further  shown  by  the  following  experiments  : — 

Exp.  ii. — Fasten  a  piece  of  barky  charcoal  to  a  stout  wire  ; 
pass  the  wire  through  a  small  flat  board  or  a  piece  of  tinplate. 
Kindle  the  charcoal  by  holding  it  in  a  flame ;  then  hang  it  in  a 


Oxygen — Properties.  23 

jar  of  oxygen.  It  will  burn  away  rapidly,  with  a  steady  glow, 
throwing  out  sparks,  or  scintillations,  and  will  produce  a  new 
colourless  gas,  called  carbonic  anhydride,  or  carbonic  acid 
(C02). 

Exp.  12. — Place  a  little  sulphur  in  a  small  copper  spoon  on 
the  end  of  a  wire,  called  a  deflagrating  spoon  ;  heat  it  in  the  flame 
of  a  spirit  lamp  till  it  takes  fire,  and  suspend  it  in  like  manner  in 
another  jar  of  oxygen.  The  sulphur  will  burn  with  a  lilac  flame, 
and  on  uniting  with  the  gas  will  form  an  invisible  substance  with 
a  pungent  odour,  called  sulphurous  anhydride  (SO2). 

Exp.  13. — Cut  off  a  piece  of  phosphorus  of  about  the  size  of 
a  pea  from  a  stick  of  phosphorus  under  water.*  Dry  it  care- 
fully on  a  bit  of  blotting-paper,  and  put  it  into  a  copper  spoon, 
also  suspended  from  a  wire.  Touch  it  with  a  hot  wire  :  it  will 
take  fire.  Plunge  it  at  once  into  oxygen  :  it  will  burn  with 
dazzling  brilliancy,  and  form  white  fumes  of  phosphoric 
anhydride  (PaO5). 

Many  substances  which  will  scarcely  burn  in  air  deflagrate, 
or  burn  with  violence,  in  oxygen  : — 

.  Exp.  14, — Heat  a  piece  of  watch-spring  red  hot  for  a  few 
moments  in  the  fire ;  let  it  cool,  and  then  twist  it  into  a  spiral. 
Heat  one  end  slightly,  and  dip  it  into  a  little  powdered 
sulphur,  and  pass  the  other  end  through  a  cork.  Set  fire 
to  the  sulphur,  and  immediately  plunge  it  into  a  jar  of  oxygen, 
supporting  it  in  the  neck  of  the  jar  by  the  cork.  The 
burning  sulphur  will  set  fire  to  the  steel,  which  will  burn  with 
great  splendour,  while  drops  of  melted  oxide  of  iron  (Fe3O4)  will 
run  down  and  fall  upon  the  plate  below. 

Exp.  15. — Zinc  foil  cut  into  the  form  of  a  tassel,  if  it  be 
tipped  with  sulphur  to  enable  it  to  take  fire,  may  be  kindled  and 
will  burn  in  oxygen  with  a  dazzling  white  light,  forming  zinc 
oxide  (ZnO). 

Exp.  1 6. — Place  a  piece  of  potassium  f  of  the  size  of  a  pea  in 

*  Phosphorus  is  extremely  inflammable  ;  it  must  always  be  kept  under 
water,  and  should  not  be  handled  with  the  warm  hand  except  under 
water. 

H"  Potassium  is  the  metal  contained  in  pearl-ash ;  it  must  always  he 
kept  under  naphtha,  and  must  not  be  touched  with  the  fingers,  or  with 
anything  that  is  wet. 


24  Oxidation —  Combustion. 

a  copper  spoon;  heat  it  in  the  flame  of  a  spirit  lamp  till  it  be- 
gins to  glow ;  then  introduce  it  into  a  jar  of  oxygen.  It  will 
burn,  and  a  quantity  of  white  solid  potash  (KaO)  will  be  formed 
in  the  spoon  by  the  union  of  oxygen  with  the  potassium. 

The  compounds  which  oxygen  forms  with  other  elements 
are  called  oxides,  and  the  act  of  combination  of  any  substance 
with  oxygen  is  called  oxidation.  The  experiments  above 
described  are  instances  of  this  process,  and  in  each  case  a 
compound  is  produced  entirely  different  in  properties  both 
from  the  oxygen  and  from  the  body  burned. 

(9)  Combustion. — Whenever  any  rapid  chemical  action 
takes  place,  attended  with  great  heat  and  light,  combustion  is 
said  to  occur.  In  order  to  start  the  process,  it  is  generally 
necessary  to  heat  the  body;  afterwards  the  heat  given  out  by 
the  chemical  change  produced  is  more  than  enough  to  carry 
it  on,  and  the  combination  goes  forward  with  increasing 
vigour  until  it  is  completed. 

Bodies  which  are  burned,  and  which  disappear  from  sight 
— as  when  coal  or  charcoal  is  consumed  in  the  fire — are  in 
no  case  actually  destroyed.  They  are  only  altered  in  form. 
A  candle,  for  example,  in  burning  seems  to  be  completely 
consumed,  but  the  materials  of  which  it  consisted  are  not 
destroyed.  This  most  important  fact  may  be  proved  as " 
follows : — 

Exp.  17. — Take  a  glass  tube  30  or  40  centim.  long  and  4  cm. 
in  diameter.  Thrust  a  piece  of  wire  gauze  half-way  down  the 
tube,  and  fill  the  upper  half  with  fragments  of  caustic  soda 
(Fig.  7).  To  the  lower  end  of  the  tube  a  fit  a  cork  pierced  with 
three  or  four  holes  for  the  admission  of  air,  and  fasten  to  it  a 
short  piece  of  wax  taper.  To  the  other  end  of  the  tube  fit  a  cork 
through  which  a  short  tube  of  about  8  millimetres  in  diameter  is 
passed.  Now  weigh  the  tube  and  its  contents.  By  means  of  a 
piece  of  india-rubber  tubing,  join  the  short  tube  at  the  top  with 
a  closed  jar  filled  with  water,  which  is  to  act  as  an  aspirator. 
This  is  easily  made  from  a  tinplate  9-litre  (2 -gallon)  oil  can  b, 
into  the  side  of  which,  near  the  bottom,  a  small  cock  is  soldered. 
Open  the  stop-cock  near  the  bottom  of  the  closed  jar,  and  let 


Matter  when  Burnt  not  Destroyed.  25 

the  water  flow.  The  water  cannot  run  out  at  the  stop-cock 
unless  air  takes  its  place  ;  and  since  the  aspirator  is  connected 
by  the  caoutchouc  tubing  with  the  wide  glass  tube,  which  is  open 
freely  to  the  outer  air  at  the  bottom,  a  current  of  air  is  esta- 
blished through  the  wide  tube.  Now  withdraw  the  cork  at  the 
bottom,  light  the  taper,  and  immediately  put  it  back  into  the 


tube.  In  three  or  four  minutes'  time  close  the  stop-cock  :  the 
taper  will  at  once  go  out.  When  the  apparatus  is  cold,  slip 
off  the  caoutchouc  connecting  tube,  and  weigh  the  wide  glass 
tube.  It  will  be  found  to  have  gained  in  weight  by  several 
decigrams. 

The  candle  in  burning  combines  with  a  portion  of  oxygen 
from  the  air,  forming  water  and  carbonic  anhydride.  These 
are  both  absorbed  as  they  pass  over  the  caustic  soda,  and 
hence,  though  the  taper  itself  looks  smaller,  and  has  really 
lost  in  weight,  the  chemical  products  obtained  weigh  more 
than  the  taper  originally  did. 

Whether  a  body  be  burned  quickly  or  slowly,  the  quantity 
of  heat  which  a  given  weight  of  it,  say  i  grain,  gives  out  in 
burning  is  perfectly  fixed,  and  depends  upon  the  nature  of 


26  Combustion — Quick,  Slow. 

the  burning  body.  Nevertheless,  the  more  the  oxygen  is 
diluted  by  mixture  with  a  gas  which  does  not  act  chemi- 
cally upon  it,  such  as  nitrogen,  the  lower  is  the  actual 
temperature  which  is  produced  at  the  moment  by  combus- 
tion; because  not  only  are  fewer  particles  of  oxygen  in 
contact  with  the  burning  body,  but  at  the  same  time  the 
diluting  gas  carries  off  part  of  the  heat,  since  it  has  its  own 
temperature  raised  without  contributing  to  the  chemical 
action.  And  hence,  when  a  body  is  burned  in  air,  it  seems 
to  give  out  much  less  heat  than  when  burned  in  oxygen,  and 
it  burns  much  more  slowly.  But  when  we  blow  a  fire  with 
the  bellows,  or  cause  a  powerful  draught  of  air  up  the 
chimney,  w-e  quicken  the  combustion  and  raise  the  heat, 
because  we  thus  bring  a  larger  number  of  particles  of 
oxygen  into  contact  with  the  fuel  in  a  given  time  ;  and 
by  the  same  operation  we  carry  off  the  gases  formed  by 
combustion,  which  are  unable  to  combine  with  the  burning 
body,  and  would  prevent  its  contact  with  fresh  particles  of 
the  oxygen  of  the  air.  That  this  is  so  may  be  seen  by  the 
check  to  the  fire  and  the  reduced  consumption  of  fuel 
caused  by  closing  the  damper  or  shutting  the  ashpit  door  of 
a  furnace. 

Oxygen  is  the  most  important  and  also  the  most  abundant 
of  the  elements.  We  have  already  seen  (Exp.  5),  that  it 
forms  a  little  more  than  a  fifth  of  the  bulk  of  the  air ;  it 
also  constitutes  eight-ninths  of  the  entire  weight  of  water  ; 
while  clay,  limestone,  and  siliceous  sand  contain  about  half 
their  weight  of  it.  Oxygen  is  also  found  largely  in  various 
other  common  substances  not  of  mineral  origin,  such  as 
sugar,  starch,  and  woody  fibre,  which  contain  about  half 
their  weight  of  it ;  and  many  bodies  derived  from  animals, 
such  as  muscular  tissue,  leather,  and  horn,  contain  it  in 
large  proportion. 

Oxygen  may  be  shaken  up  with  water  without  experiencing 
any  sensible  change  in  bulk,  for  it  is  only  slightly  soluble  in 
that  liquid,  100  cub.  centim.  of  it,  at  15°  C.,  dissolving  about 


Oxygen,  Test  for  it. 


27 


Fig.  8. 


3  c.c.  of  the  gas;  but  this  solubility,  slight  as  it  may  appear,  is 
essential  to  the  existence  of  living  animals,  for  it  is  only  in  the 
dissolved  state  that  the  gas  finds  its  way  into  the  blood,  and 
effects  the  chemical  changes  in  the  body  necessary  to  life, 
both  in  land  animals  and  in  those  which  live  in  water. 
A  solution  of  potash  may  also  be  shaken  up  with  oxygen  with- 
out sensibly  dissolving  it ;  but  if  pyrogallic  acid  be  added 
to  the  potash  solution,  the  oxygen  is  rapidly  absorbed,  and 
the  liquid  turns  brown. 

Exp.  1 8. — Pass  a  few  bubbles  of  oxygen  into  a  strong  tube, 
graduated  to  divisions  of  O'5  c.  c.  each,  filled  with  mercury,  and 
placed  in  a  deep  glass  full  of  mercury  (Fig.  8).  Introduce  a 
solution  of  potash  (i  part  of  solid  potash  in  4  of  water)  by  means 
of  a  pipette  with  a  point 
curved  upwards,  blowing  into 
the  pipette  with  sufficient 
force  to  drive  over  8  or  10 
drops  of  the  solution.  Agitate 
this  liquid  briskly  with  the  gas 
by  thrusting  the  tube  down 
quickly  into  the  mercury,  and 
raising  it  to  its  former  level 
several  times.  The  oxygen 
will  not  alter  in  volume.  Now, 
with  a  fresh  pipette,  intro- 
duce an  equal  quantity  of  a 
solution  of  pyrogallic  acid 
(i  part  of  acid  and  6  of 
water).  Again  agitate  the  mix- 
ture. It  becomes  intensely 
brown,  and  the  whole  of  the 
gas  will  disappear  if  pure. 
If  a  measured  quantity  of 
air  be  taken,  it  is  easy  in 

a  few  minutes  to  ascertain  roughly  the  proportion  of  oxygen 
present  by  the  absorption  effected  in  this  way,  because  the 
nitrogen  is  left  unchanged,  and  may  be  measured  after  the 
absorption  of  oxygen  is  over. 


28  Measurement  of  Gases. 

Oxygen  is  a  little  heavier  than  atmospheric  air.  A 
measure  of  air  which  weighs  i  gram  would,  if  filled  with 
oxygen  at  the  same  temperature,  and  when  the  baro- 
meter stands  at  the  same  height,  weigh  1-1056  gram;  and  a 
measure  of  hydrogen  which  weighs  i  gram  would,  when 
filled  with  oxygen,  weigh  exactly  16  grams  :  so  that  oxygen 
is  precisely  16  times  as  heavy  as  hydrogen. 

(10)  Measurement  of  Gases  under  Standard  Conditions. — 
It  is  necessary  when  comparing  the  weights  of  gases  with 
each  other  to  attend  carefully  to  the  temperature.  A  quan- 
tity of  any  gas  which  at  o°  C.  exactly  fills  i  litre -expands  so 
rapidly  when  heated,  that  at  273°  C.  it  would  become  dilated 
to  2  litres.  A  quantity  of  any  gas  which  at  o°  C.  measures 
just  i  litre  would,  if  heated  to  ioo°C.  (the  temperature  of 
boiling  water),  become  expanded  to  1*366  litre.  It  is  now 
customary  to  compare  gases  at  the  standard  temperature  of 
o°C.;  or,  if  they  are  not  actually  at  this  temperature,  to  re- 
duce the  results  to  this  point  by  calculation.  For  instance, 
if  v  be  the  volume  of  any  gas  measured  at  the  temperature  t 
in  Centigrade  degrees,  and  V  be  the  bulk  of  the  same  gas  at 
o°  C.,  then— 

r==  273  y  ^ 

273+'* 

It  is  equally  important  to  compare  gases  at  a  fixed  baro- 
metric pressure.  At  the  level  of  the  sea,  the  average  weight 
of  a  column  of  air  which  reaches  to  the  top  of  the  atmosphere 
will  exactly  balance  a  column  of  mercury  760  millimetres 
high,  and  at  o°  C.  But  at  the  top  of  a  mountain  of  a  little 
more  than  5-5  kilometres  or  nearly  3*4  miles  high,  the  weight 
of  a  column  of  air  reaching  to  the  top  of  the  atmosphere 
would  only  be  able  to  balance  a  column  of  mercury  of  half 
this  height,  or  380  mm.  And  a  quantity  of  air  at  the  bottom 
of  the  mountain  which  measures  i  litre  while  the  barometer 
stands  at  760  mm.  would,  if  carried  to  the  top  of  the  moun- 
tain, expand  to  2  litres.  But  it  is  not  necessary  to  take  the 
air  to  the  top  of  the  mountain  in  order  to  observe  this  fact : 


Measurement  of  Gases.  29 

for  if  the  pressure  upon  the  gas  be  by  any  other  suitable 
means  lessened  to  one-half,  the  air  will  immediately  become 
doubled  in  bulk.  If,  on  the  other  hand,  the  pressure  be 
doubled,  the  air  will  become  reduced  in  bulk  to  one-half. 
Gases,  in  fact,  occupy  a  space  inversely  as  the  pressure  to 
which  they  are  subjected  ;  and,  in  order  to  avoid  inaccuracy 
in  measuring  them,  they  are  always  compared  by  calculating 
them  as  if  subjected  to  a  fixed  or  standard  pressure  of  a 
column  of  mercury  at  o°  C.  of  760  mm.  high. 

Suppose  v  to  be  the  observed  volume  (after  it  has  been 
corrected,  if  necessary,  for  temperature),/  the  pressure  at 
the  time  of  observation,  measured  by  the  height  of  the  mer- 
curial column  in  the  barometer  in  millimetres,  and  Fthe 
volume  corrected  to  the  pressure  of  760  mm.  of  mercury, 
then— 

y—tlL. 

760' 

In  taking  the  specific  gravity  of  gases,  it  has  been  the 
practice  to  compare  them  with  an  equal  bulk  of  dry  air  as 
the  standard.  When,  for  instance,  it  is  said  that  the  specific 
gravity  of  oxygen  is  1-10563,  the  expression  means  that  if 
a  vessel  which  holds  a  certain  volume  of  dry  air  which 
weighs  exactly  i  grain,  were  filled  with  dry  oxygen  gas, 
at  the  same  temperature  and  pressure,  the  weight  of  this 
oxygen  would  be  1-10563  gram;  the  same  bulk  of  dry 
hydrogen  would  be  only  -0691  gram,  and  the  specific  gravity 
of  hydrogen  is  said  to  be  '0691. 

This  practice  of  comparing  gases  with  air  is  both  cus- 
tomary and  convenient;  but  it  has  been  objected  to  on  the 
ground  that  air  is  a  mixture,  and  not  a  true  chemical  com- 
pound. Now  the  proportions  of  the  substances  in  a  mixture 
are  liable  to  variation,  while  those  of  a  chemical  compound 
are  invariable.  Fortunately  for  the  accuracy  of  the  data 
founded  on  comparison  with  the  air  as  a  standard,  the  pro- 
portions of  the  oxygen  and  nitrogen  in  the  air  do  not  vary 
practically  to  any  important  amount,  but  the  objection  in 


3O  Measurement  of  Gases. 

principle  remains.  Hence  it  has  of  late  years  become  the 
custom  further  to  compare  the  weights  of  gases  and  vapours 
with  the  weight  of  an  equal  volume  of  some  elementary 
body  ;  and  the  element  selected  for  the  purpose  is  hydrogen, 
the  lightest  of  all  known  substances.  The  result  of  this 
comparison  with  hydrogen  will  hereafter  be  spoken  of  as  the 
relative  weight  of  a  gas  or  vapour.  Suppose  that,  for  the 
purpose  of  this  comparison,  we  take  a  vessel  which  would  hold 
i  gram  of  hydrogen  at  o°  C.  and  760  mm.  barometer  ;  the 
capacity  of  such  a  vessel  would  be  1 1*19  litres.  This  measure, 
when  filled  with  oxygen  under  similar  circumstances,  would 
contain  1 6  grams  of  oxygen;  and  if  rilled  with  nitrogen,  it 
would  contain  14  grams  of  nitrogen.  Hence,  if  the  weight  of 
such  a  bulk  of  hydrogen  be  called  i,  the  relative  weight  of  oxy- 
gen will  be  16,  the  relative  weight  of  nitrogen  14,  and  so  on, 

(n)  Adds,  Bases,  and  Salts. — The  compounds  formed  by 
the  union  of  oxygen  with  the  other  elements  differ  from  each 
other  very  much  in  properties ;  but  among  them  are  two  im- 
portant classes  of  oxides,  chemically  opposed  to  each  other, 
one  commonly,  but  erroneously,  known  as  acids,  the  other 
as  bases.  Everyone  is  familiar  with  the  sourness  of  vinegar 
or  of  a  lemon,  which  in  both  cases  is  due  to  the  presence  of 
a  substance  known  in  chemical  language  as  an  acid.  The 
acetic  acid  gives  the  sour  taste  to  vinegar ;  the  citric  acid  is 
the  substance  which  gives  the  sharp  flavour  to  the  lemon. 
There  are  many  other  well-known  substances,  like  sulphuric, 
nitric,  and  phosphoric  acids,  which  when  diluted  sufficiently 
to  prevent  them  from  injuring  the  surface  of  the  tongue,  pos- 
sess a  sour  taste  ;  and  these  all  belong  to  the  class  of  acids. 

Again,  most  persons  are  acquainted  with  the  nauseous 
taste  of  soda,  and  with  the  peculiar  soapy  feeling  which  it 
occasions  when  rubbed  upon  the  skin :  this  is  due  to  what 
is  called  the  alkaline  property  of  soda,  a  property  in  which 
it  resembles  potash  and  a  few  other  substances.  The 
alkalies  are  soluble  in  water,  and  form  one  class  of  a  numerous 
group  of  chemical  agents,  known  under  the  name  of  bases. 


A  cids  and  A  Ikalies.  3 1 

Many  elementary  substances,  like  sulphur  and  phosphorus, 
by  their  combination  with  oxygen,  furnish  compounds  which 
are  freely  soluble  in  water,  and  have  a  sour,  and  often  a 
burning,  taste  ;  they  also  turn  many  vegetable  blue  colours, 
such  as  the  blue  of  an  infusion  of  litmus,*  or  of  purple 
cabbage,  to  a  bright  red.  Such  oxides  are  called  anhydrides 
(which  means  bodies  free  from  hydrogen)  to  distinguish 
them  from  the  bodies  these  same  oxides  furnish  when  they 
are  acted  upon  by  water,  which  all  contain  hydrogen,  and 
belong  to  the  class  of  acids.  All  the  non-metallic  elements, 
except  hydrogen  and  fluorine,  form  with  oxygen  one  or 
more  compounds,  which,  when  dissolved  in  water,  produce 
acids,  and  often  intensely  powerful  acids.  Many  of  the 
metals,  on  the  other  hand,  by  their  union  with  oxygen,  give 
rise  to  bodies  of  an  opposite  kind,  which  have  been  termed 
bases.  For  instance,  the  white  alkaline  substance  formed  by 
burning  potassium  in  oxygen  is  dissolved  rapidly  by  water ; 
it  produces  a  colourless  liquid,  of  a  soapy,  disagreeable  taste, 
and  a  peculiar  lixivial  smell.  It  corrodes  the  skin,  dissolves 
oil-paint,  restores  the  blue  colour  to  litmus  which  has  been 
reddened  by  an  acid,  and  neutralises  the  strongest  acids.  This 
power  which  acids  and  bases  have  of  reacting  upon  each  other, 
and  destroying  the  chemical  activity  which  each  has  when 
separate,  is  the  most  marked  feature  of  these  two  classes  of 
substances.  The  compounds  produced  by  their  action  upon 

*  Paper  tinged  blue  with  a  watery  or  spirituous  infusion  of  litmus  (a 
colouring  matter  obtained  from  certain  lichens)  is  in  constant  use  for 
showing  the  presence  of  an  acid  in  a  liquid,  as  it  immediately  becomes 
reddened  by  the  action  of  even  very  small  quantities  of  an  acid  when 
uncombined  with  a  base.  The  same  paper,  if  faintly  reddened  by  means 
of  vinegar  or  any  other  acid,  is  equally  valuable  as  a  test  for  an  alkali, 
which  if  present  uncombined  with  acids  immediately  restores  the  blue 
colour.  The  alkalies  also  turn  paper  tinged  yellow  with  the  colouring 
matter  of  turmeric  or  rhubarb  to  a  reddish-brown  hue. 

A  test  in  chemistry  simply  means  a  method  of  trial,  and  test  solutions 
or  test  papers,  are  solutions  or  papers  made  for  the  purpose  of  trying 
whether  certain  substances  are  present  or  not,  according  as  the  solu- 
tion or  paper  does  or  does  not  undergo  a  particular  change,  which  would 
be  produced  if  the  body  sought  for  were  there. 


32  Acids y  Bases,  Salts. 

each  other  constitute  what  are  called  salts,  and,  when 
freed  from  the  water  in  which  they  are  dissolved,  may  often 
be  obtained  in  crystals. 

Exp.  19. — Cut  a  red  cabbage  into  slices,  and  boil  it  with 
water ;  strain  off  the  purplish  liquid  thus  obtained.  To  a  portion 
of  this  decoction  add  a  little  solution  of  caustic  potash  :  a  green 
liquid  will  be  produced.  To  another  portion  of  the  cabbage 
liquor  add  a  few  drops  of  sulphuric  acid  :  the  solution  will 
become  red.  Pour  the  red  acid  liquor  into  the  green  alkaline 
solution,  and  stir  the  mixture  :  the  red  colour  at  first  disappears, 
and  the  whole  remains  green ;  but  on  continuing  to  add  the  red 
liquid  cautiously,  a  point  is  reached  at  which  the  liquid  assumes 
a  clear  blue  colour.  There  is  then  no  excess  either  of  acid  or  of 
alkali  in  the  solution ;  and  on  evaporating  the  liquid  a  neutral 
salt,  potassic  sulphate,  formed  by  the  action  of  the  acid  upon  the 
alkali,  may  be  obtained  in  the  form  of  crystals.* 

Here  it  is  necessary  to  remark  that  the  same  element  often 
forms  more  than  one  oxide  which  when  dissolved  in  water, 
furnishes  an  acid.  When  this  is  the  case,  the  oxide  which 
contains  the  largest  quantity  of  oxygen  is  designated  by  a 
name  ending  in  ic,  while  the  compound  with  the  smaller 
proportion  of  oxygen  is  made  to  end  in  ous.  Sulphur,  for 
example,  furnishes  both  sulphuric  acid  (H2SO4)  and  sulphur- 
ous acid  (H2SO3)  ;  and  both  these  acids  form  salts  when  acted 
upon  by  bases.  The  salts  of  acids  ending  in  ic  are  indicated 
by  names  which  end  in  ate,  while  the  salts  of  acids  in  ous 
have  names  ending  in  ite.  For  instance,  the  salts  of  sul- 
phuric acid  are  called  sulphates ;  of  nitric  acid,  nitrates ;  of 
phosphoric  acid,  phosphates ;  while  those  of  sulphurous 

*  The  change  may  be  expressed  in  symbols  in  this  manner : — 
Sulphuric  Acid  Caustic  Potash  Potassic  Sulphate  Water 

H,SO4  +       2KHO       =  K2SO4          4        2HZO 

2x1  +  32  +  16x4      2(39+1  +  16)     2x39  +  32+16x4     2(1x2+16) 

from  which,  by  reference  to  the  table  of  atomic  weights  (page  5)>  it 
may  be  seen  that  98  grams  of  pure  sulphuric  acid,  with  112  grams  of 
caustic  potash,  would  form  174  grams  of  a  neutral  salt,  and  would  set 
free  36  grams  of  water. 


Names  given  to  Acids  and  Bases.  33 

acid  are  called  sulphites ;  those  of  nitrous  acid,  nitrites ;  and 
of  phosphorous  acid,  phosphites. 

The  acids  are  not  all  soluble  in  water ;  and  the  insoluble 
acids  have  no  sour  taste.  In  like  manner  bases  exist,  such  as 
zinc  oxide  and  ferric  oxide,  which  are  not  soluble  in  water, 
and  then  they  neither  corrode  the  skin  nor  exert  any  sensible 
effect  upon  coloured  tests  ;  but  they  are  capable  of  reacting 
chemically  with  acids,  and  forming  salts. 

Exp.  20. — Add  zinc  oxide  to  diluted  sulphuric  acid  and  stir 
the  two  together  :  it  will  be  readily  dissolved,  and,  on  evaporat- 
ing the  liquid,  a  true  salf,  zinc  sulphate,  may  be  obtained  in 
needle-shaped  crystals  : — 

Sulph.  Acid         Zinc  Oxide  Zinc  Sulphate  Water 

H,SO4     +     ZnO       =       ZnSO4     +     HZO 

Sometimes  the  same  metal,  when  combined  with  different 
quantities  of  oxygen,  furnishes  two  different  bases,  or  bodies 
capable  of  neutralising  acids  more  or  less  completely.  Iron, 
for  instance,  furnishes  ferric  oxide  (Fe2O3)  and  ferrous  oxide 
(FeO)  j  mercury  also  gives  mercuric  oxide  (HgO)  and  mer- 
curous  oxide  (Hg2O).  The  base  to  which  the  name  ending  in 
ic  is  given  always  contains  the  larger  proportion  of  oxygen. 
A  compound  formed  by  the  action  of  ferrous  oxide  on  sul- 
phuric acid  would  be  called  ferrous  sulphate ;  while  that 
furnished  by  the  action  of  ferric  oxide  on  sulphuric  acid 
would  be  known  as  ferric  sulphate. 

Besides  the  oxides  which  furnish  acids  and  bases,. there  is 
a  third  set  of  oxides,  which  is  neither  acid  nor  basic,  and  is 
not  disposed  to  enter  into  combination  with  either  class. 
Black  manganese  oxide  (MnO2 ;  or,  as  would  be  better,  by 
doubling  the  molecular  formula,  MnO,  MnO3),  magnetic 
iron  oxide  (FeO,  Fe2O3),  and  red  lead  (2PbO,  PbO2),  afford 
instances  of  this  kind.  Such  oxides  appear  generally  to  be 
formed  by  the  union  of  two  different  oxides  of  the  same 
metal  with  each  other,  and  are  analogous  to  salts.  Indeed, 
the  union  of  an  anhydride  with  an  anhydrous  (or  water  free) 

D 


34  Ozone. 

basic  oxide  furnishes  a  true  salt ;  for  instance,  sulphuric  an- 
hydride (SO3),  by  uniting  with  cupric  oxide  (CuO),  furnishes 
cupric  sulphate  (CuO,SO3,  or  CuSO4,  as  it  is  usually  written) ; 
but  in  such  cases  no  separation  of  water  occurs. 

(12)  Ozone. — Oxygen  in  its  usual  form  has  no  sensible 
smell,  but  it  may  be  obtained  in  a  more  active  condition, 
and  then  it  has  a  very  peculiar  odour.  This  smell  is  per- 
ceived whenever  an  electrical  machine  is  put  in  action  in  the 
air,  and  more  or  less  ozone  (as  it  has  been  called  from  the 
Greek  ofw,  I  smell)  is  immediately  produced.  It  is  also 
formed  whenever  water  is  decomposed  between  platinum 
plates  by  the  voltaic  battery  (p.  44).  A  special  form  of 
apparatus  has  been  contrived  for  electrifying  a  current  of 
air,  so  as  to  change  part  of  its  oxygen  into  ozone.  Ozone 
may  also  be  obtained  by  chemical  means. 

Exp.  21. — Scrape  off  the  white  coating  of  a  stick  of  phospho- 
rus under  water,  and  cut  the  cleansed  phosphorus  into  pieces 
12  or  15  millim.  long.  Place  one  of  these  pieces  in  a  wide- 
mouthed  litre  bottle  full  of  air,  with  about  a  teaspoonful  of  water 
at  the  bottom.  Close  the  mouth  of  the  bottle  with  a  glass 
plate,  and  expose  the  whole  for  half  an  hour  to  a  temperature  of 
15°  or  20°  C.  Then  invert  the  neck  of  the  bottle  in  water,  and 
allow  the  phosphorus  to  fall  out.  Replace  the  glass  plate,  and 
withdraw  the  bottle  and  its  contents  from  the  water.  The 
phosphorus  in  this  experiment  undergoes  a  slow  oxidation, 
during  which  a  little  ozone  is  formed,  and  is  left  mixed  with  the 
air ;  but  the  ozone  will  be  again  destroyed  if  it  is  left  too  long 
with  the  phosphorus. 

The  most  delicate  test  of  ozone  is  potassic  iodide  (KI), 
from  which  it  immediately  sets  iodine  free,  which  can  in- 
stantly be  detected  by  its  action  on  starch. 

Exp.  22. — Boil  a  gram  of  starch  in  50  grams  of  water,  so  as 
to  produce  a  thin  mucilage,  and  add  o-i  gram  of  potassic  iodide 
to  the  mixture.  Brush  a  little  of  this  solution  over  a  slip  of 
clean  writing-paper,  and  plunge  the  paper  into  one  of  the  jars  in 
which  the  phosphorus  has  been  acting  on  the  air.  An  imme- 


Ozone.  35 

diate  blue  stain  is  produced,  owing  to  the  action  first  of  the 
ozone  upon  the  iodide,  and  then  of  the  free  iodine  upon  the 
starch.  Paper  may  be  prepared  beforehand  with  this  starch 
paste  and  iodide,  and  dried  ;  in  which  form  it  may  be  kept  in  a 
bottle  till  wanted. 

The  ozone  displaces  iodine  from  the  iodide,  though  ordi- 
nary oxygen  will  not  do  so. 

The  slow  oxidation  of  ether,  of  oil  of  turpentine,  and  of 
many  other  substances,  is  attended  with  the  formation  of 
small  quantities  of  ozone  ;  and  most  plants,  when  growing  in 
the  sunshine,  give  it  out  in  excessively  small  quantities. 
Traces  of  ozone  are  probably  present  usually  in  the  air,  but 
the  proportion  varies.  If  a  piece  of  the  dry  iodized  paper 
be  exposed  for  five  minutes  in  the  open  air  of  the  countiy,  it 
acquires  a  bluish  tint,  the  strength  of  which  varies  on  dif- 
ferent days,  according  as  the  quantity  of  ozone  in  the  air  is 
greater  or  less.  Sometimes,  in  damp  or  foggy  weather,  no 
such  change  occurs,  and  it  is  scarcely  ever  observed  in  the 
air  of  large  towns.  The  effect  is  most  marked  on  the  sea 
coast,  and  when  the  wind  blows  off  the  sea.  It  is  not  im- 
probable that  these  minute  quantities  of  ozone  exert  an 
important  purifying  effect  upon  the  atmosphere  by  destroying 
and  oxidising  animal  effluvia,  which  would  otherwise  in- 
crease in  quantity  until  they  produced  disease.  The  ozone 
is  absorbed  by  these  offensive  bodies,  which  it  converts  into 
harmless  compounds. 

Ozone  is  not  soluble  in  water,  but  it  at  once  corrodes 
caoutchouc,  cork,  and  many  other  organic  matters.  It  pro- 
duces a  feeling  of  irritation  in  the  lungs  when  air  strongly 
charged  with  it  is  breathed.  It  immediately  oxidizes  the 
common  metals,  as  well  as  mercury,  when  dry,  and  even 
silver,  if  it  be  moist.  It  is  instantly  changed  into  common 
oxygen,  if  passed  over  manganese  oxide,  on  which,  however, 
it  produces  no  permanent  effect.  Several  other  bodies  also 
on  which  it  exerts  no  sensible  action  change  it  into  common 
oxygen ;  and  if  it  be  heated  to  a  temperature  not  greater 


36  Ozone. 

than  that  of  boiling  water,  a  similar  change  occurs.  Ozone 
is  much  denser  than  oxygen  gas  :  three  measures  of  oxygen 
furnish  by  condensation  two  measures  of  ozone.  The  exact 
amount  of  condensation  cannot  be  found  directly,  because 
ozone  has  never  been  obtained  free  from  admixture  with  a 
very  large  proportion  either  of  air  or  of  oxygen. 

Ozone  has  a  powerful  bleaching  action.  It  has  been 
attempted  to  make  ozone  by  electric  action  on  the  air,  and 
to  use  the  product  as  a  bleaching  agent. 

Exp.  23. — Take  a  bottle  of  air  which  has  been  ozonised  by 
means  of  phosphorus,  and  add  to  it  a  few  drops  of  a  very  dilute 
blue  solution,  formed  by  dissolving  powdered  indigo  in  strong 
sulphuric  acid,  and  then  diluting  it  with  water.  If  the  blue 
liquid  is  shaken  up  with  the  ozonised  air,  the  colour  quickly  dis- 
appears. 

The  mode  in  which  electricity  and  phosphorus,  and  other 
agents,  act  upon  oxygen  and  convert  it  into  ozone  is  not 
understood. 

(13)  NITROGEN:  Symbol  N;  Atomic  Wt.  14;  Atomic 
Vol.  Q  ;  Sp.  Gr.  0-971  ;  Rel.  Wt.  14;  MoL  Wt.  N2,  28  ; 

Moi.  vol.  m. 

The  most  abundant  constituent  of  the  atmosphere,  nitro- 
gen (the  '  generator  of  nitre,'  so  called  because  it  is  an  es- 
sential component  in  nitre)  is  also  sometimes  called  azote, 
because  it  is  unfit  to  support  life. 

The  easiest  methods  of  obtaining  nitrogen  are  founded 
upon  the  removal  of  oxygen  from  the  air.  One  of  these, 
the  exposure  of  moistened  iron  filings  to  air  contained  in  a 
jar  over  water,  has  been  already  described  (Exp.  4). 

Exp.  24. — Support  a  stick  of  phosphorus  upon  a  wire  above 
the  surface  of  a  dish  of  water,  and  place  a  jar  of  air  over  it.  The 
phosphorus  will,  without  the  aid  of  heat,  gradually  remove  the 
oxygen  from  the  air,  forming  phosphorous  anhydride  (PaO3), 
which  will  be  dissolved  by  the  water,  and  in  a  day  or  two  the 
gas  which  is  left  will  be  nitrogen  nearly  pure. 


Nitrogen.  37 

Exp.  25. — The  same  change  may  be  effected  in  a  few  minutes 
if  the  phosphorus  is  heated.  Dry  two  or  three  pieces  of  phos- 
phorus of  the  size  of  a  pea  upon  blotting-paper,  and  float  them 
in  a  small  porcelain  dish  upon  the  water  in  the  trough :  kindle  the 
phosphorus  by  touching  it  with  a  hot  wire,  and  cover  it  at  once 
with  a  jar  full  of  air.  The  phosphorus  will  burn  till  it  has 
exhausted  all  the  oxygen  in  the  jar,  which  will  become  filled  with 
white  fumes  of  phosphoric  anhydride  (P*O5).  These  become 
gradually  dissolved  by  the  water,  and  nearly  pure  nitrogen  is  left. 

Oxygen  may  also  be  very  completely  separated  from 
nitrogen  by  allowing  the  air  to  stream  very  slowly  over  finely 
divided  copper  made  red  hot. 

Nitrogen  has  neither  colour,  taste,  nor  smell.  It  has 
never  been  liquefied  by  cold  or  pressure.  It  is  a  little 
lighter  than  air.  A  measure  of  hydrogen  which  would  weigh 
i  gram  would,  when  filled  with  nitrogen  at  the  same  tem- 
perature and  pressure,  weigh  14  grams.  Water  dissolves  it 
but  sparingly,  taking  up  about  one-fiftieth  of  the  bulk  of  the 
gas.  Nitrogen  alone  is  unfit  for  the  support  of  life,  but  it 
is  not  a  direct  poison,  and  is,  indeed,  constantly  inhaled 
when  mixed  with  oxygen,  the  activity  of  which  it  serves  to 
moderate. 

Exp.  26. — Plunge  a  lighted  taper  into  a  jar  of  nitrogen  :  the 
gas  does  not  take  fire,  but  the  light  is  put  out  instantly. 

Nitrogen  offers  a  striking  contrast  in  properties  to  oxygen. 
It  has  scarcely  any  tendency  to  unite  directly  with  any  of 
the  elements  except  boron,  titanium,  and  one  or  two  of  the 
rarer  metals.  Yet  it  is  one  of  the  most  widespread  forms  of 
matter ;  it  is  found  in  the  free  state  in  the  air,  as  well  as  in 
combination  in  some  of  the  most  active  and  important  com- 
pounds— such,  for  instance,  as  in  nitric  acid,  which  is  obtained 
from  the  nitre  of  commerce,  and  in  ammonia  or  hartshorn. 
Though  not  abundant  in  plants,  it  is  never  quite  wanting  in 
them.  It  also  forms  part  of  the  strongest  vegetable  poisons 
and  medicines,  such  as  prussic  acid,  strychnia,  and  morphia ; 
and  it  is  a  component  of  some  of  the  most  important 


38  Nitrogen — Other  Components 

articles  of  food,  such  as  bread,  milk,  and  the  flesh  of 
animals.  The  compounds  which  nitrogen  forms  with  each 
of  the  other  elements  are  called  nitrides,  and  animal  sub- 
stances which  contain  nitrogen  are  often  spoken  of  as 
azotised  substances. 

(14)  Air  a  Mixture  of  Several  Gases. — 

Exp.  27. — Measure  off  into  a  jar  over  water  210 -c.  c.  of  oxygen, 
and  add  to  it  790  c.  c.  of  nitrogen;  then  introduce  a  lighted 
taper.  I  twill  continue  to  burn  as  in  ordinary  air. 

Such  a  mixture  might  be  breathed  with  perfect  safety,  and 
would  possess  most  of  the  properties  of  the  air.  The  atmo- 
sphere is  in  fact  a  true  mixture  of  several  gases,  among 
which  nitrogen  and  oxygen  are  by  far  the  most  abundant. 
Though  these  two  gases  are  not  chemically  united  in  the 
atmosphere  with  each  other,  yet  in  the  open  air  they  are 
found  to  be  mixed  in  very  uniform  proportions.  Careful 
analyses  of  numerous  specimens  of  air  taken  from  the  most 
distant  parts  of  the  earth  furnish  results  the  extremes  of 
which  do  not  vary  from  one  another  in  the  proportion  of 
oxygen  more  than  about  i  part  in  200,  and  generally  the 
variation  is  much  less.  The  samples  were  taken,  amongst 
other  places,  from  Port  Bowen,  amidst  the  perpetual  ice  of 
the  Arctic  Circle ;  from  Vera  Cruz,  the  hotbed  of  yellow 
fever  ;  from  the  summits  of  the  Andes  in  the  western  hemi- 
sphere, and  of  the  Alps  in  the  eastern;  from  the  higher 
regions  of  the  atmosphere  in  balloons,  as  well  as  from  the 
streets  of  the  crowded  capitals  of  Europe,  such  as  London, 
Paris,  Berlin,  and  Madrid.  Supposing  all  the  ingredients 
of  the  air  except  nitrogen  and  oxygen  to  have  been  removed 
by  proper  means,  it  has  been  found  that  i  litre,  or  1000  c.  c., 
of  the  mixture  would  contain  on  the  average  209*5  c<  c-  °f 
oxygen  and  790*5  c.  c.  of  nitrogen.  If  the  quantities  be 
determined  by  weight,  instead  of  by  measure,  1000  grams  of 
the  mixture  would  contain  232*2  grams  of  oxygen  and 
767*8  grams  of  nitrogen. 


of  A  tmospheric  A  ir.  39 

But  it  is  easy  to  show  that  air  always  contains  other  sub- 
stances besides  oxygen  and  nitrogen. 

Exp.  28. — Pour  a  little  clear  lime-water  into  a  saucer,  and 
leave  it  for  a  few  minutes.  A  white  skin  or  film  will  gradually 
be  formed  upon  the  surface,  and  this  if  shaken  will  sink  to  the 
bottom ;  a  fresh  film  will  then  be  formed  in  its  place,  and  if  this 
be  disturbed  it  will  again  be  renewed,  until  the  whole  of  the  lime 
has  been  separated  from  its  solution  in  the  form  of  this  white 
substance,  which  has  the  chemical  composition  of  chalk,  or  calcic 
carbonate. 

In  this  experiment  the  lime  has  taken  up  from  the  air  one 
of  the  less  abundant  gases  which  it  contains,  and  to  this  gas 
the  name  of  carbonic  acid  or  carbonic  anhydride  (CO2)  has 
been  given.  The  quantity  of  this  gas  is  always  small.  It 
varies  in  i  litre,  or  1000  c.  c.,  of  air  from  0*3  to  0*6  c.  c.,  so 
that  10,000  measures  of  air  contain  from  3  to  6  measures  of 
this  gas. 

Exp.  29. — Pour  some  water  into  a  glass  tumbler,  taking  care 
to  keep  the  outside  dry  ;  place  in  the  water  a  lump  of  ice.  In 
the  course  of  .a  few  minutes  the  water  will  have  become  cooled 
by  the  melting  ice,  and  the  cooling  effect  will  extend  to  the 
outer  surface  of  the  glass,  while  dew  or  moisture  will  be  de- 
posited upon  it,  owing  to  the  condensation  of  viewless  watery 
vapour  from  the  air. 

This  experiment  shows  the  presence  of  steam  in  the  atmo- 
sphere. The  proportion  of  watery  vapour,  however,  varies 
greatly  from  time  to  time,  being  much  less  during  the  frosts 
of  winter  than  it  is  in  the  hot  weather  of  summer.  In  this 
climate  loooc.  c.  of  air  seldom  contain  more  than  20  c.  c. 
of  invisible  vapour,  and  the  proportion  ordinarily  found  in  a 
litre,  or  1000  c.  c.,  may  be  roughly  reckoned  at  14  c.  c. 

The  weight  of  a  litre  of  dry  air  free  from  carbonic  anhy- 
dride, at  o°  C.  when  the  mercury  in  the  barometer  stands  at 
760  mm.,  has  been  found  to  be  1*2932  gram. 

It  must  also  be  added  that  variable  traces  both  of  am- 
monia and  of  nitric  acid  are  found  in  the  air,  but  the  pro- 


4O   Less  abundant  Components  of  Atmospheric  Air. 

portions  are  so  minute  that  they  cannot  be  detected  unless 
very  large  quantities  of  air  are  examined ;  and  these  sub- 
stances are  more  easily  found  in  the  rain,  which,  by  falling 
through  large  tracts  of  air,  has  dissolved  them,  and  brought 
them  down  with  itself.  Minute  as  the  quantity  is  which  is 
found  even  then,  they  have  important  uses  in  supplying 
what  is  needful  for  the  health  of  growing  plants. 

In  large  towns  small  quantities  of  other  gases  are  likewise 
occasionally  met  with,  such  as  sulphurous  anhydride  (SO2), 
derived  from  the  pyrites  in  the  coal  consumed,  and  sul- 
phuretted hydrogen  (H2S),  from  the  putrefaction  of  animal 
refuse. 

Besides  these  gaseous  bodies,  minute  particles  of  solid 
matter  are  always  suspended  in  the  air;  these  are  of  the 
most  varied  kinds,  and  among  them  are  the  spores  and 
seeds  of  minute  fungi  and  plants.  These  particles  are  so 
small  that  they  commonly  escape  notice ;  under  favourable 
circumstances  they  may  be  easily  seen,  as  they  form  the 
1  motes '  which  appear  to  be  dancing  in  the  sunbeams  when 
they  find  their  way  into  a  darkened  room. 

The  average  composition  of  a  litre,  or  1000  c.  c.,  of  air 
may  be  represented  as  follows,  in  measure  of  each  in- 
gredient : — 

Cub.  Centim. 

Oxygen 206*1 

Nitrogen 779'5 

Aqueous  Vapour  (about)        .         .  14*0 

Carbonic  Anhydride      ...  *4 
Nitric  Acid   .        .         \ 

Ammonia      .,!•..  traces 
Carburetted  Hydrogen  J 

1000*0 


CHAPTER  III. 

WATER — HYDROGEN. 

(15)  WATER:    Symbol,  H2O ;  Atomic  and  MoL  Wt.  18  j 

Sp.  gr.  of  liquid  at  4°  C.  rooo;  Sp.  gr.  of  ice,  0*918;  Sp.  gr. 
of  steam,  0-622  ;  Rel.  Wt.  9;  Atomic  and  MoL  Vol.  \    \    [. 

Until  about  a  hundred  years  ago  this  wonderful  and  uni- 
versally diffused  liquid  was,  like  the  air,  supposed  to  be  one 
of  the  elements  of  nature ;  but  we  can  now  easily  prove 
that  it  is  a  compound  body,  and  can  both  separate  it  into 
its  elements,  and  reproduce  it  from  those  elements  by  causing 
them  again  to  combine  together. 

Exp.  30. — Throw  a  small  piece  of  the  metal  potassium  into  a 
saucer  containing  water,  and  retreat  to  a  little  distance.  As  the 
metal  is  lighter  than  water,  it  will  rise  to  the  surface,  where  it 
will  seem  to  burst  into  flame,  rolling  rapidly  about  until  it  dis- 
appears with  a  slight  report.  Now  place  a  piece  of  reddened 
litmus  paper  in  the  water  :  it  will  become  blue,  showing  that 
the  potassium  has  combined  with  oxygen,  which,  as  we  shall 
see,  is  derived  from  the  water,  and  has  been  by  it  converted  into 
the  alkaline  body  potash  (Exp.  16). 

Exp.  31. — Roll  upon  the  end  of  a  cedar  pencil  a  piece  of  wire 
gauze  about  4  centim.  square,  and  fold  up  the  end  of  the  cylin- 
der thus  formed;  twist  a  piece  of  copper  bell-wire  25  or  30 
centim.  long  round  the  little  cage,  so  as  to  form  a  handle  ;  then 
introduce  into  it  one  or  two  small  pieces  of  sodium,  the  metal 
contained  in  common  salt,  and  pass  the  cage  quickly  beneath 
the  mouth  of  a  small  glass  jar  filled  with  water,  and  inverted  in 
water  :  bubbles  of  gas  will  be  formed  at  once,  and  will  continue 
to  rise  into  the  jar  until  all  the  sodium  has  disappeared.  Now 
close  the  jar  with  a  glass  plate,  withdraw  it  from  the  water,  and 
apply  a  light.  The  gas  will  take  fire,  and  burn  with  a  pale 
flame. 

To  this  substance  the  name  of  hydrogen  (water-producer) 
has  been  given.  It  is  regarded  as  an  elementary  body. 


42     '  Decomposition  of  Water. 

The  results  of  these  experiments  may  be  thus  explained  : 
Water  is  a  compound  of  oxygen  and  hydrogen.  The 
potassium  or  the  sodium  displaces  a  part  of  the  hy- 
drogen from  the  water,  forming  potash  or  soda,  which 
is  dissolved  by  the  water,  while  the  hydrogen  escapes  in 
the  gaseous  form,  as  may  be  explained  by  the  following 
equation : — 

Water  Potassium  Potash  Hydrogen 

2HaO         +       Kz  2KHO         +     Ha 

2(2xl  +  l6)  2x39  2(39+1  +  16)  2x1 

36  78  112  2 

114  114 

When  potassium  is  used,  the  hydrogen  becomes  so  much 
heated  at  the  moment  when  it  is  set  free  that  it  takes  fire  in 
the  air  at  once ;  but  when  the  sodium  is  kept  under  water, 
the  hydrogen  is  prevented  from  mixing 
with  the  air  till  it  becomes  cool,  and 
then  it  does   not    burn   till   a  light  is 
applied  to  it. 

If  a  small  voltaic  battery  can  be  had. 
it  is  easy  to  obtain  both  the  oxygen 
and  the  hydrogen  from  the  water  at 
the  same  time. 

Exp.  32. — Select  two  pieces  of  glass 
tube  of  equal  diameter,  about  12  centim. 
long  and  12  mm.  wide,  and  open  at  both 
ends.  Fit  a  cork  into  one  end  of  each, 
and  pass  a  stout  platinum  wire,  ending  in  a  small  plate  of 
platinum,  through  each  cork,  so  as  to  reach  nearly  to  the 
open  end  of  the  tube.  Then  cover  each  cork  neatly  with  a 
solution  of  sealing-wax  in  spirit  of  wine,  and  let  it  dry.  Next 
fill  each  tube  with  water  slightly  acidulated  with  sulphuric 
acid  *  (about  I  part  of  acid  in  30  of  water),  and  invert  it  in 

*  Much  heat  is  given  out  whenever  strong  sulphuric  acid  is  mixed 
even  with  cold  water.  When  this  mixture  is  to  be  made,  the  water 


Decomposition  of  Water.  43 

a  glass  of  the  same  acidulated  water  (Fig.  9).  Connect  one 
of  the  platinum  wires  with  the  wire  proceeding  from  one  of 
the  poles  of  a  properly  charged  voltaic  battery,  which  may 
consist  of  three  or  four  cells  made  on  Grove's  plan  (see  treatise 
on  '  Electricity  '),  and  connect  the  other  platinum  wire  with  the 
remaining  pole  of  the  battery.  Gas  will  begin  at  once  to  rise 
from  both  plates,  and  will  collect  in  the  tubes  :  one  of  these  tubes 
will  receive  just  twice  as  much  gas  in  the  same  time  as  the  other. 
When  sufficient  gas  has  been  collected,  remove  the  tube  with  the 
smaller  quantity  of  gas,  closing  it  with  the  thumb  before  lifting 
it  out  of  the  water.  Turn  it  mouth  upwards,  and  introduce  a 
splinter  of  wood  red-hot  at  the  point.  .  It  will  be  rekindled. 
This  we  know  is  a  characteristic  property  of  oxygen.  Now 
remove  the  other  tube  in  a  similar  manner,  and  apply  a  lighted 
taper.  The  gas  will  take  fire,  and  burn  with  the  pale  flame  pecu- 
liar to  hydrogen. 

In  this  experiment  it  is  to  be  noted  that  for  each  cubic 
centimetre  of  oxygen  obtained  from  the  water  2  c.  c.  of 
hydrogen  have  been  procured.  Further,  it  may  be  easily 
shown  that  these  two  gases  may  be  made  to  combine  again 
chemically  in  the  same  proportions,  and  that  they  then 
reproduce  water.  For  this  purpose  the  last  experiment  must 
be  altered  in  form  as  follows  :  — 


33-  —  Fit  a  good  cork  to  the  neck  of  a  bottle  which  will 
hold  100  c.  c.  ;  adjust  a  tube,  bent  as  in  Fig.  10,  to  the  cork, 
having  its  lower  end  turned  upwards,  and  pass  the  wires  con- 
nected with  the  two  platinum  plates  through  the  cork,  taking 
care  that  the  metals  do  not  touch  each  other.  Nearly  fill  the 
bottle  with  water  slightly  acidulated  with  sulphuric  acid,  and 
insert  the  cork  with  its  bent  tube  and  platinum  plates.  Connect 
each  plate  with  one  of  the  wires  of  the  voltaic  battery,  as  before  ; 
allow  the  air  in  the  tube  to  be  displaced  by  the  gas,  and  then 
collect  the  mixed  gases,  as  they  rise  from  both  plates,  in  a  strong 

should  be  placed  in  a  jug  or  earthenware  vessel  ;  it  should  be  stirred 
round  and  round  with  a  glass  rod,  and  the  acid  should  be  poured  into  the 
ivater  (not  the  water  into  the  acid)  in  a  slender  stream,  the  whole  being 
kept  stirred  till  the  mixture  is  complete.  ^ 


44  Decomposition  of  Water. 

dry  tube  filled  with  mercury,  and  supported  in  a  wooden  vice, 
and  inverted  in  a  small  Wedgwood- ware  mortar  containing  mer- 
cury. When  the  tube  has  become  full  of  gas,  close  the  end  of  it 
with  the  finger,  raise  it  out  of  the  mercury,  and  apply  a  light : 

Fig.  ra 


a  sharp  report  will  be  heard ;  the  two  gases  will  suddenly  unite, 
and  the  sides  of  the  tube  will  become  dewed  with  moisture, 
showing  that  water  has  been  formed  by  the  union  of  the  oxygen 
and  hydrogen. 

Another  mode  of  making  this  important  experiment  will 
be  described  when  we  come  to  treat  of  hydrogen. 

Each  litre  of  oxygen  gas  unites  with  exactly  two  litres  of 
hydrogen ;  and  if  the  gases  be  heated  to  above  100°  C.  before 
causing  them  to  unite,  and  the  heat  be  kept  up  to  the  same 
point  after  they  have  united,  exactly  two  litres  of  steam  or 
watery  vapour  will  be  obtained.  Hence,  in  representing  the 
composition  of  water  by  symbols,  its  formula  is  written  H2O, 
and  its  combining  number  is  18.  When  converted  into 
vapour  9  grams  of  water  furnish  a  bulk  of  steam  exactly 
equal  to  that  of  i  gram  of  hydrogen  at  the  same  temperature 
and  pressure  ;  so  that  the  relative  weight  of  steam  is  9,  and 
the  specific  gravity  of  steam  is  0-622;  or  the  weight  of  a 
quantity  of  steam,  compared  with  that  of  a  quantity  of  air 
which  weighs  i  gram  at  the  same  temperature  and  pressure, 
is  0-622  gram.  It  is  also  convenient  to  bear  in  mind  that 
i  litre  of  water  will  at  100°  furnish  1696  litres  of  steam,  of 


Freezing  and  Boiling  of  Watet .  45 

an  elasticity  sufficient  to  balance  the  pressure  of  a  column  of 
mercury  of  760  millimetres,  i  cubic  inch  of  water  producing 
nearly  a  cubic  foot  of  steam. 

Pure  water  has  neither  taste  nor  smell,  and  it  is  generally 
supposed  to  be  colourless,  though  when  seen  through  a 
depth  of  5  or  6  metres  it  has  a  delicate  and  faint  tinge  of  blue. 
When  cooled  sufficiently,  it  becomes  converted  into  the 
transparent  solid  form  of  ice.  The  point  at  which  pure  ice 
melts,  or  the  freezing  point,  as  it  is  usually  called,  always 
occurs  at  exactly  the  same  temperature,  if  the  ice  is  not 
exposed  to  pressure.  Hence  the  melting  point  of  ice  has 
been  made  the  starting  point  or  o°,  the  zero,  as  it  is  termed, 
of  the  centigrade  thermometric  scale.*  Again,  if  the  tem- 
perature of  water  be  raised  sufficiently  high,  the  liquid 
assumes  the  form  of  gas,  while  bubbles  of  steam  rise  through 
the  heated  liquid  and  break  upon  its  surface,  passing  off  as 
invisible  vapour.  The  water  is  said  to  boil,  and  its  vapour 
is  then  of  an  elastic  force  just  sufficient  to  balance  the  pres 
sure  of  the  air  upon  its  surface,  whatever  that  pressure  may 
be.  The  temperature  at  which  pure  water  boils  under  equal 
pressures  is  found  to  be  quite  as  uniform  as  its  freezing 
point.  This  boiling  point  of  water  serves,  therefore,  as  a 
second  fixed  point  upon  the  thermometric  scale,  and  it  has 
been  agreed  to  call  the  point  at  which  the  mercury  stands 
in  boiling  water  100°  on  the  centigrade  scale;  the  observa- 
tion being  always  made  when  the  pressure  of  the  air  upon 
the  surface  of  the  boiling  water,  as  indicated  by  the  baro- 
meter, is  equal  to  that  of  a  mercurial  column  760  mm.  long 
when  measured  at  o°  C.  One  degree  of  the  centigrade  scale 
represents  the  looth  part  of  the  apparent  expansion  of  the 
mercury  in  the  thermometer  between  the  freezing  and  the 
boiling  points  of  water,  f 

*  If  the  water  holds  salts  dissolved  in  it,  the  freezing  point  is  lowered 
to  an  extent  depending  on  the  quantity  and  kind  of  salt. 

t  If  salts  are  present  in  the  water,  the  boiling  point  may  be  raised 
several  degrees,  the  amount  varying  according  to  he  quantity  and  kind 
of  salt  in  solution. 


46  Evaporation  of  Water. 

But  water  evaporates,  or  slowly  passes  off  into  the  air  in 
the  invisible  form  of  vapour  or  steam  at  all  temperatures 
— even  from  ice  itself;  and  this  evaporation  is  going  on 
more  or  less  actively  almost  everywhere  upon  the  surface  of 
the  earth,  so  that  the  air  is  at  all  times  charged  with  moisture, 
the  proportion  of  which  is  perpetually  varying.  In  dry 
weather  the  quantity  of  vapour  found  is  always  less  than 
that  which  could  exist  unseen  in  the  air  at  the  time.  It  is 
owing  to  this  circumstance  that  wet  bodies,  when  exposed  to 
the  air,  become  dry  in  a  few  hours.  By  the  process  of 
evaporation  from  the  surface  of  the  land,  as  well  as  of  the 
ocean,  a  natural  distillation  and  purification  of  water,  of  the 
utmost  importance,  is  always  taking  place  around  us.  The 
water  discharged  by  rivers  into  the  sea  returns  unperceived 
into  the  air.  The  vapour  is  at  first  unseen,  but  as  it  rises 
into  the  colder  regions  of  the  atmosphere  it  is  condensed 
into  masses  of  visible  cloud.  These  at  last  become  too 
heavy  to  stay  aloft.  High  ridges  or  mountains  are  especially 
active  in  arresting  the  clouds,  which  then  fall  in  showers, 
and  supply  the  high  lands  with  water.  This  flows  down  the 
sides  of  the  hills,  collects  into  rivulets,  and  these  again  into 
rivers ;  or  else  the  water  sinks  into  the  earth  through  the 
porous  strata,  and  passes  down  until  it  meets  with  a  bed  of 
clay  or  some  stratum  through  which  water  cannot  pass.  The 
liquid,  when  thus  stopped,  flows  along  over  the  face  of  the 
imbedded  stratum  until  it  reaches  the  surface  of  the  soil  at 
some  lower  level  in  the  valley,  where  it  bursts  forth  in  the 
form  of  a  spring. 

Water  exhibits  a  remarkable  exception  to  the  law  of  con- 
traction by  the  removal  of  heat,  which  all  other  bodies  obey. 
When  exposed  to  a  falling  temperature,  it  diminishes  in 
bulk  regularly  till  it  has  become  cooled  down  to  4°  C.  ;  and 
then,  instead  of  contracting,  it  begins  slowly  to  expand,  and 
continues  to  do  so  until  it  reaches  the  freezing  point,  when 
the  ice  which  is  formed  suddenly  expands  still  more.  This 
exceptional  expansion  of  water  as  it  cools  is  attended  with 


Maximum  Density  of  Water.  47 

very  important  consequences  to  our  well  being.  During  the 
frosts  of  winter  a  rapid  process  of  cooling  occurs  from  the 
surface  of  all  lakes  and  streams ;  the  colder  water  sinks  to 
the  bottom  until  the  whole  has  become  reduced  to  4°  C., 
but  below  this  point  the  colder  water  becomes  the  lighter, 
and  remains  at  the  top,  so  that  it  protects  the  mass  beneath 
from  the  winter  cold.  In  this  way  it  prevents  such  a  reduc- 
tion of  temperature  in  deep  pools  as  would  be  fatal  to  fishes 
and  aquatic  animals.  The  ice  also  floats  upon  the  surface, 
and  thus  the  bottoms  of  lakes  and  rivers  are  preserved  from 
the  accumulation  of  masses  of  ice,  which,  if  it  sank  as  fast 
as  it  is  formed,  could  never  be  melted  even  by  the  summer's 
sun. 

The  temperature  of  4°  C.  is  that  at  which  water  is  heavier 
than  at  any  other,  and  is  hence  called  its  point  of  maximum 
density.  A  litre  of  water  at  this  temperature  weighs  exactly 
1000  grams,  or  i  kilogram.  Water  is  773  times  as  heavy  as 
air  at  o°  C.,  when  the  barometer  is  at  760  mm.  In  taking 
the  specific  gravity  of  solids  and  of  liquids,  they  are  always 
compared  with  the  weight  of  an  equal  bulk  of  pure  water  at 
4°  C.  For  example,  if  gold  be  said  to  have  a  specific  gravity 
of  19*34,  it  is  meant  that  i  c.  c.  of  water  at  4°  weighs  i  gram, 
while  a  cub.  centim.  of  gold  at  the  same  temperature  weighs 
19-34  grams. 

In  order  to  obtain  pure  water  for  this  and  various  other 
purposes,  it  must  be  distilled.  This  is  usually  performed  by 
means  of  a  still  and  worm-tub  ;  but  if  these  be  not  at  hand, 
a  small  quantity  of  water  may  be  distilled  in  the  following 
manner : — 

Exp.  34. — Procure  a  clean  tinplate  9-litre  (or  2-gallon)  oil  can ; 
bend  a  glass  tube  into  the  form  shown  in  Fig.  1 1  ;  adapt  it  to  a 
sound  bung  which  exactly  fits  the  neck  of  the  can,  and  fill  the 
can  about  two-thirds  full  of  water.  Then  adjust  the  bent  tube 
to  the  condenser  shown  in  the  figure.  Place  the  can  upon  the 
fire,  and  heat  it  till  the  water  boils  steadily,  whilst  a  small 
stream  of  cold  water  is  kept  running  through  the  outer  tube  of  the 


48  Distillation  of  Water. 

condenser.  Allow  the  water  as  it  distils  over  from  the  can  to 
flow  into  a  flask  placed  for  its  reception.  Throw  away  the  first 
40  or  50  cub.  cm.,  which  are  apt  to  contain  a  little  ammonia  and 
semi-gaseous  impurities,  Then  collect  3  or  4  litres.  This  will 
be  distilled  water ;  and  if  the  experiment  is  performed  carefully, 

Fig.  n. 


the  liquid  so  condensed  will  be  pure  from  all  solid  substances  in 
solution.  A  few  drops  when  allowed  to  evaporate  from  a  slip  of 
clean  glass  will  leave  scarcely  a  perceptible  mark  behind ;  but 
if  a  few  drops  of  the  water  before  distillation  be  so  treated,  a 
distinct  residue  will  be  obtained.  A  sufficient  condenser  maybe 
made  without  difficulty  as  follows  : — Select  a  piece  of  glass  tube 


Rain  Water.  49 

of  about  80  centim.  in  length  and  2  centim.  in  diameter ;  fit  it 
by  means  of  corks  into  a  second  tube  of  glass  or  of  tinplate 
about  60  centim.  in  length  and  4  centim.  in  diameter.  Into  the 
space  between  the  two  tubes  pass  a  bent  quill  tube  through  one 
of  the  corks,  and  introduce  through  the  other  cork  a  second 
similar  tube  ;  cold  water  is  to  be  supplied  through  the  tube  at 
the  lower  end,  while  the  hot  water  runs  off  at  the  upper  end,  as 
shown  in  the  figure. 

Water,  in  consequence  of  its  extensive  power  of  dis- 
solving bodies  of  various  kinds,  is  not  met  with  naturally 
in  a  state  of  perfect  purity.  Rain  water,  collected  in  the 
open  country  after  continued  wet  weather,  is  nearly  pure ; 
but  even  this  contains  the  gases  of  the  atmosphere  dis- 
solved in  it,  usually  to  the  extent  of  from  about  30  to  50 
c.  c.  in  a  litre  of  water,  besides  particles  of  solid  suspended 
matters. 

The  presence  of  air  in  water  is  necessary  to  the  life  of 
fishes  and  aquatic  animals  generally,  for  it  is  by  means  of 
the  oxygen  thus  dissolved  that  they  maintain  respiration. 
Its  presence  may  be  shown  as  follows  : — 

Fig.  12. 


Exp.  35. — Fit  a  quill  tube,  a  (Fig.  12),  by  means  of  a  sound  cork 
to  a  Florence  flask,  having  first  filled  the  flask  with  rain  water, 
or  with  spring  water ;  fill  the  tube  also  completely  with  water, 
and  adapt  it  to  a  small  glass  jar,  b,  also  filled  with  water,  and 
standing  in  the  water-trough.  Heat  the  water  in  the  flask  till  it 

E 


5O  Impurities  which  occur 

boils  briskly;  bubbles  of  air  will  gradually  be  driven  out  of  the 
water,  and  may  be  collected  in  the  glass  receiver,  b. 

Rain  water  which  falls  in  mountainous  or  rocky  districts 
formed  of  millstone  grit,  mica  slate,  and  other  rocks 
which  contain  but  little  soluble  material,  generally  runs 
off  nearly  free  from  anything  except  a  little  vegetable 
matter  and  dissolved  gases ;  but  spring  water,  although  it 
may  be  perfectly  colourless  and  transparent,  contains  some 
salts  in  solution.  The  quantity  and  the  kind  of  these 
salts  varies  with  the  kind  of  rock  or  soil  in  which  the  spring 
originates. 

The  salts  most  often  found  in  spring  water  are  sodic 
chloride  or  common  salt,  calcic  carbonate  from  chalk, 
and  calcic  sulphate,  as  well  as  small  amounts  of  magnesic 
carbonate  and  sulphate.  The  waters  of  town  wells  also 
generally  contain  traces  of  ammonia,  and  more  or  less  of  the 
nitrates  and  nitrites  of  calcium  or  of  sodium.  The  nitric 
acid  in  these  salts  is  the  result  of  the  gradual  oxidation  of 
the  drainage  from  animal  refuse,  which,  though  in  its  recent 
state  one  of  the  most  noxious  impurities  that  can  be  found 
in  water,  yet  when  completely  oxidized  into  nitrates  is  no 
longer  dangerous  to  health.  Nearly  all  spring  waters 
contain  also  a  very  small  quantity  of  silica  in  solution. 
Wholesome  waters  do  not  contain  in  solution  more  than 
one  gram  of  saline  substances  per  litre;  and  the  most 
highly  prized  sources  contain  but  a  few  centigrams  only  in  a 
litre  of  water. 

Exp.  36. — Select  a  thin  porcelain  dish  which  will  hold  60  or 
80  cub.  cm. ;  place  it  in  one  pan  of  the  balance,  and  cut  a  piece  of 
lead  till,  when  placed  in  the  other  scale-pan,  it  counterpoises  or 
exactly  balances  the  dish.  Measure  off  half  a  litre  of  spring 
water,  and  pour  some  of  this  water  into  the  weighed  dish  ;  place 
it  over  a  very  small  gas  flame,  so  as  to  evaporate  the  water  gently 
without  allowing  it  to  boil ;  add  the  rest  of  the  water  from  time 
to  time  until  the  half  litre  has  been  completely  evaporated  away. 
Dry  the  salts  thus  obtained,  and  weigh  what  is  left  as  accurately 


in  Natural   Waters.  51 

as  you  can.  By  multiplying  this  quantity  by  2  you  will  obtain 
the  amount  of  soluble  solid  substances  per  litre  which  that  par- 
ticular specimen  of  water  contained. 

This  is  the  basis  of  the  plan  which,  with  many  additional 
precautions,  is  adopted  for  determining  the  quantity  of  salts 
in  the  process  of  analysing  waters  to  be  used  for  drinking  or 
manufacturing  purposes. 

River  water  often  holds  a  smaller  proportion  of  salts  dis- 
solved in  it  than  spring  water ;  and  yet  it  may  be  less  fit  for 
drinking,  for  it  generally  contains  a  much  larger  quantity  of 
organic  matter ;  that  is  to  say,  it  contains  a  larger  propor- 
tion of  soluble  drainage  products  of  a  vegetable  or  animal 
nature,  which  have  been  washed  off  the  surface  of  the 
soil  by  the  rain,  or  which  have  been  emptied  from  sewers 
into  the  stream. 

Such  sewerage  products  should  not  be  allowed  to  escape 
into  rivers  until  they  have  been  more  or  less  purified  by 
allowing  the  liquid  to  run  over  cultivated  land,  which  is 
manured  by  it  in  its  progress.  The  liquid  afterwards  runs 
away  comparatively  harmless. 

Happily  for  mankind,  running  water  is  endowed  with 
a  considerable  amount  of  purifying  power,  due  to  the 
oxygen  of  the  air  which  it  holds  in  solution.  Vegetable 
matters  consist  almost  entirely  of  carbon,  oxygen,  and 
hydrogen,  with  a  very  small  proportion  of  nitrogen ;  whilst 
animal  matters,  in  addition  to  carbon,  oxygen,  and  hydro- 
gen, contain  a  considerable  proportion  of  nitrogen  ;  both 
vegetable  and  animal  matter  likewise  contain  a  little  sulphur, 
either  as  sulphates  or  in  some  other  form.  During  putre- 
faction these  organic  bodies  give  out  a  disgusting  odour, 
and,  if  swallowed  in  this  state,  even  when  largely  diluted  with 
water,  may  cause  serious  illness.  By  the  action  of  the 
oxygen  dissolved  in  the  water,  the  hydrogen  of  these  com- 
pounds becomes  changed  into  water,  the  carbon  into  car- 
bonic acid,  and  most  of  the  nitrogen  into  nitric  acid.  The 
continual  motion  of  the  water  exposes  fresh  surfaces  to  the 

E  2 


52  Impurities  found  in    Water. 

air;  fresh  oxygen  is  in  consequence  always  being  absorbed, 
and  the  oxidation  which  takes  place  is  generally  sufficient 
to  preserve  the, stream  in  a  wholesome  state.  But  if  the 
water  be  overloaded  with  organic  refuse,  or  if  it  become 
stagnant,  the  whole  of  the  dissolved  oxygen  may  become 
absorbed  by  the  decaying  matter  without  renewal  from  the 
air,  and  the  pool  will  then  emit  an  offensive  odour,  and  may 
become  a  centre  of  disease.  The  nitration  through  the  well 
aerated  porous  soil  which  water  naturally  undergoes  before 
it  issues  in  the  form  of  springs,  is  attended  with  an  oxidizing 
and  purifying  action  of  the  highest  importance. 

River  water  should  always  be  filtered  through  sand  or 
through  a  charcoal  filter  before  it  is  used  for  drinking. 
Suspended  matters,  such  as  clay,  fish  spawn,  or  small 
animals  may  be  thus  removed,  but  the  salts  in  solution  are 
not  sensibly  affected  by  such  filtration. 

Exp.  37. — Dissolve  0*395  gram  of  potassic  permanganate  in 

1  litre  of  water,  and  add  3  c.  c.  of  this  solution  to  a  mixture  of 

2  c.  c.  of  dilute  sulphuric  acid  (40  of  water  and  I  of  acid)  with 
half  a  litre  of  distilled  water,  in  a  glass  flask,  so  as  to  give  the 
liquid  a  distinct  purplish  tinge ;  little  or  no  change   of  colour 
will  be  seen  at  the  end  of  three  hours,  if  the  mixture  be  left 
to  itself.     Do  the   same  thing  with  an  equal  quantity  of  river 
water :  in  three  hours'  time  the  tint  will  have  become  reddish 
or  brownish,  if  any  considerable  quantity  of  organic  matter  be 
dissolved  in  the  water. 

The  foregoing  result  may  be  thus  explained  :  The  sul- 
phuric acid  separates  permanganic  acid  from  the  salt,  and  in 
the  presence  of  organic  matter  this  acid  loses  a  portion  of  its 
oxygen,  which  combines  with  the  constituents  of  the  organic 
matter,  while  the  permanganic  acid  becomes  converted  into 
a  compound  of  manganese  of  a  different  and  less  intense 
colour,  and  containing  less  oxygen. 

A  weak  solution  of  the  permanganate,  indeed,  furnishes 
a  valuable  comparative  test  of  the  fitness  of  water  for 
drinking.  If  the  permanganate  does  not  alter  sensibly  in 


Hard  and  Soft   Water.  53 

colour  in  such  an  experiment,  there  is  no  organic  impurity 
to  be  feared  in  the  water. 

Water  is  commonly  spoken  of  as  hard  or  soft,  according 
to  its  action  upon  soap.  Soap  is  a  combination  of  a  fatty 
or  oily  acid  with  soda ;  and  this  compound  is  readily  soluble 
in  pure  water.  Waters  which  contain  salts  of  calcium  or 
magnesium  cause  the  soap  to  curdle,  since  these  metals 
furnish  with  the  fatty  acid  of  the  soap  compounds  which 
are  not  soluble  in  water.  Such  waters  are  said  to  be  hard. 
Soap  which  is  thus  curdled  is  consumed  in  waste.  In  such 
water  soap  neither  cleanses  nor  produces  a  lather  until  the 
whole  of  the  earthy  salts  have  been  decomposed  and  an  ex- 
cess of  soap  is  present.  Soft  waters,  on  the  contrary,  do  not 
contain  these  earthy  salts,  and  they  dissolve  the  soap  without 
difficulty,  and  without  destroying  either  its  cleansing  power 
or  its  tendency  to  form  a  lather. 

Many  waters  exhibit  what  is  called  temporary  hardness; 
such  waters  become  softer  by  boiling.  The  hardness  in  this 
case  is  due  to  the  presence  of  calcic  or  magnesic  carbonate. 
These  compounds  are  scarcely  soluble  at  all  in  pure  water, 
but  they  become  soluble  to  a  considerable  extent  in  water 
charged  with  uncombined  carbonic  acid.  When  such  waters 
are  boiled,  the  carbonic  acid  is  driven  off  by  the  heat,  and 
the  calcic  and  magnesic  carbonates  which  the  acid  had  dis- 
solved become  deposited,  and  a  '  fur'  or  incrustation  takes 
place  on  the  inside  of  the  boiler,  as  may  be  seen  by  examin- 
ing a  kettle  used  for  boiling  such  waters. 

Exp.  38. — Place  half  a  litre  of  a  water  of  the  kind  just  referred 
to,  such  as  that  of  the  Thames  or  of  the  New  River,  in  a  glass 
flask,  and  boil  it  over  a  lamp  for  a  quarter  of  an  hour  :  little 
crystalline  grains  of  the  earthy  carbonates  which  were  in  solution 
will  gradually  be  deposited,  and  the  water  will  be  found  to 
be  considerably  softened. 

Exp.  39. — Mix  another  half  litre  of  such  a  water  before  it  is 
boiled  with  about  one-eighth  of  its  bulk  of  limewater.  The 
liquid  will  become  turbid,  and  on  standing  for  a  few  hours,  till  it 
is  clear,  it  will  be  found  to  be  much  softer  than  before. 


54  Soap-test  for   Water. 

The  reason  of  this  result  is,  that  the  lime  in  the  limewater 
has  combined  with  the  carbonic  acid  which  the  river  water 
held  dissolved.  Chalk  is  thus  formed,  and  at  the  same  time 
the  chalk  previously  dissolved  by  the  carbonic  acid  becomes 
separated ;  so  that  both  the  lime  of  the  limewater,  if  it  be 
not  added  in  too  large  a  proportion,  and  that  originally  in 
the  water  dissolved  as  chalk,  become  precipitated  *  together, 
and  the  water  is  softened. 

Exp.  40. — Prepare  a  mixture  of  about  equal  parts  of  strong 
spirit  and  water,  so  as  to  obtain  a  liquid  of  sp.  gr.  0-920,  and  in 
half  a  litre  of  this  dissolve  o-i  gram  of  curd  soap.  Into  a  glass 
bottle  fitted  with  a  stopper,  and  capable  of  holding  about  100  c.  c., 
measure  off  50  c.  c.  of  such  a  hard  water ;  then  add,  little  by 
little,  some  of  the  spirituous  solution  of  soap.  Put  the  stopper 
into  the  bottle,  and  shake  it  briskly  for  a  minute  :  no  lather  will 
be  formed  at  first,  but  the  soap  will  be  curdled.  Continue  to 
add  the  solution,  shaking  briskly  between  each  addition.  At 
length  there  will  be  more  soap  added  than  the  lime  salts  can 
decompose,  and  as  soon  as  this  happens  a  lather  will  be  formed 
in  the  bottle. 

This  is  the  principle  upon  which  Dr.  Clark's  soap  test  for 
determining  the  hardness  of  water  is  based.  In  applying 
this  test  the  strength  of  the  soap  solution  is  first  carefully 
ascertained,  and  then  the  exact  proportion  necessary  to 
produce  a  lather  is  determined  for  each  particular  water ; 
by  means  of  tables  constructed  for  the  purpose,  the  hardness 
of  the  water  is  then  easily  calculated. 

Besides  this  temporary  hardness  in  water,  there  is  a  per- 
manent form  of  hardness.  Indeed,  very  commonly  the  same 
water  exhibits  hardness  of  both  kinds.  The  amount  of  each 
may  be  found  by  applying  the  soap  test  to  the  water  before 
it  has  been  boiled,  and  again  after  boiling  it  for  half  an  hour, 

*  When  a  clear  liquid  becomes  cloudy  or  milky  from  the  addition  of 
another  clear  liquid,  the  chemical  change  is  attended  with  the  formation 
of  some  insoluble  compound,  which  is  separated,  or,  in  chemical  lan- 
guage, is  precipitated  from  the  liquid.  The  insoluble  substance  is  called 
a  precipitate ',  whether  it  sinks  to  the  bottom  or  floats  in  the  solution. 


Permanent  Hardness — Mineral  Waters.        55 

taking  care  to  add  distilled  water  if  necessary  to  supply  the 
exact  quantity  which  has  been  boiled  away. 

The  difference  between  the  hardness  of  the  water  before 
it  was  boiled  and  that  found  afterwards  gives  the  temporary 
hardness  ;  while  the  degree  of  hardness  which  remains  after 
the  boiling  represents  the  amount  of  permanent  hardness. 
This  permanent  hardness  is  due  to  the  presence  of  salts  of 
calcium  or  magnesium  other  than  the  carbonates,  such  as 
the  sulphates  or  nitrates. 

Waters  having  this  permanent  kind  of  hardness  may  be 
softened  by  a  method  well  known  in  the  laundry  ;  for  by  the 
addition  of  sodic  carbonate,  or  common  washing  soda,  the 
calcium  or  magnesium  is  precipitated  as  carbonate,  while 
sodic  sulphate  or  nitrate  remains  dissolved.  For  instance, 
with  calcic  sulphate  the  change  may  be  thus  represented  : 

Calcic  Sulphate      Sodic  Carbonate  Sodic  Sulphate     Calcic  Carbonate 

CaSO4     +     Na,CO3       =       NaaSO4     +     CaCO3 

The  sodic  sulphate  which  is  formed  does  not  curdle  the 
soap. 

Mineral  waters  hold  a  much  larger  quantity  of  substances 
in  solution  than  waters  used  for  domestic  purposes.  If  such 
waters  contain  iron,  they  have  an  inky  taste,  like  some  of 
those  at  Tunbridge  Wells.  They  are  called  chalybeate  waters, 
and  may  be  known  by  the  rusty  deposit  which  they  form  when 
exposed  to  the  air.  Others  are  strongly  effervescent,  like 
seltzer  water,  owing  to  the  escape  of  carbonic  acid ;  while 
others  have  a  strong  sulphuretted  odour,  like  the  Harrogate 
water,  owing  to  the  presence  of  sulphuretted  hydrogen. 
Others,  again,  are  strongly  saline,  like  the  springs  at  Epsom 
and  at  Cheltenham ;  whilst  in  some  cases  in  volcanic  districts, 
as  in  the  Geysers  of  Iceland,  the  water  is  actually  boiling 
hot,  and  holds  silica  dissolved ;  and  in  the  Bath  waters  the 
springs,  though  not  boiling,  are  much  hotter  than  the  surface 
of  the  soil  from  which  they  come  forth,  owing  to  the  action 
•of  subterraneous  heat. 


5  6  Saturation —  Crystallisation . 

Sea  water  is  largely  loaded  with  common  salt,  and  with 
magnesic  chloride  and  sulphate,  to  which  last  fhe  bitter  taste 
is  due.  It  contains  also  a  large  number  of  other  salts ; 
among  these  are  small  proportions  of  bromides  and  iodides. 
A  litre  of  sea  water  contains  about  37*5  grams  of  various 
salts  dissolved  in  it;  about  29  grams  of  these  consist  of 
sodic  chloride. 

Water  dissolves  certain  bodies,  such  as  common  salt, 
nitre,  and  Epsom  salt,  with  great  ease;  but  other  salts, 
such  as  calcic  sulphate,  are  soluble  in  much  smaller  pro- 
portion in  the  same  quantity  of  water.  When  water  has 
dissolved  as  large  a  proportion  of  any  substance  as  it  can 
take  up,  it  is  said  to  be  saturated  with  that  substance. 
Some  substances,  such  as  silver  chloride  and  siliceous 
sand,  are  not  soluble  in  water  to  any  sensible  extent. 
Generally  speaking,  water,  though  saturated  with  any  parti- 
cular salt  when  cold,  will  dissolve  a  larger  quantity  of  the 
same  salt  when  heated. 

Exp.  41. — Grind  up  in  a  mortar  50  or  60  grams  of  sodic  sul- 
phate with  about  twice  its  weight  of  water  at  15°  C.  The  water 
will  dissolve  a  considerable  proportion,  but  not  the  whole  of  the 
salt.  Pour  this  saturated  solution  into  a  flask,  and  warm  it 
gently ;  it  will  now  dissolve  50  grams  more  of  the  salt  without 
difficulty.  Allow  the  solution  to  cool  down  to  the  temperature 
of  the  air,  say  15°  C.  :  long  four-sided  prisms  will  crystallise 
from  the  liquid.  Pour  off  the  liquid,  and  dry  the  crystals  by 
pressing  them  between  a  few  folds  of  blotting-paper.  When 
they  appear  to  be  dry,  put  a  small  quantity  of  the  crystals  into  a 
test-tube,  and  apply  a  gentle  heat  :  the  salt  will  liquefy,  and  on 
continuing  to  apply  the  heat  a  large  quantity  of  water  will  be 
driven  off,  and  a  dry  white  powder  will  be  left  in  the  tube. 

The  water  thus  given  off  was  chemically  combined  with 
the  crystals.  Many  other  salts  which  appear  to  be  perfectly 
dry  to  the  touch,  give  off  water  when  heated,  and  crumble 
down  to  a  shapeless  mass  ;  such,  for  example,  as  alum,  cupric 
sulphate,  and  sodic  carbonate;  but  they  all  lose  the  dis- 


Efflorescent  and  Deliquescent  Salts.  57 

tinctive  form  of  their  crystals  when  the  water  has  been 
expelled.  If  the  dry  residue  be  again  dissolved  in  water, 
new  crystals  similar  to  the  original  ones  are  obtained,  and 
they  are  found  also  to  contain  water  as  before.  The  quan- 
tity of  water  is  definite  for  each  salt ;  for  instance,  sodic 
sulphate  contains  10  atoms  of  water  combined  with  each 
atom  of  the  salt,  and  its  composition  is  represented  by  the 
formula  Na2SO4,  ioH2O;  cupric  sulphate  has  5  atoms 
(CuSO4,  5H2O),  sodic  carbonate  10  atoms  to  each  atom  of 
the  salt  (Na2CO3,  ioH2O),  and  so  on.  Such  water  which  is 
necessary  to  the  form  of  the  salt,  but  which  can  be  driven 
off  without  altering  its  chemical  character,  is  called  water 
of  crystallisation.  Sometimes  mere  exposure  of  the  salt 
to  the  air  is  sufficient  to  get  rid  of  this  water  of  crystal- 
lisation. 

Exp.  42. — Take  some  of  the  fresh  crystals  of  sodic  sulphate ; 
let  them  lie  exposed  on  a  piece  of  blotting-paper  for  two  or  three 
days.  They  will  gradually  lose  their  water,  and  crumble  down, 
or  effloresce  into  a  white  powder. 

Other  salts  act  in  the  opposite  manner.  They  absorb 
moisture  from  the  air,  and  become  dissolved  in  it :  they 
deliquesce. 

Exp.  43. — Put  a  little  calcic  chloride  in  a  watch-glass,  and 
expose  it  to  the  air;  do  the  same  with  a  few  decigrams  of 
potassic  carbonate ;  in  two  or  three  days  both  salts  will  be 
found  in  a  liquid  state. 

The  compounds  of  water  are  often  called  hydrates  (from 
the  Greek  vfiwp,  water) ;  and  when  a  substance  is  entirely 
free  from  water  in  combination,  it  is  said  to  be  anhydrous. 
When  a  salt  is  dissolved  in  water,  it  is  not  considered  by  the 
act  of  solution  to  have  entered  into  true  chemical  combina- 
tion ;  the  water  and  the  salt  may  be  separated  from  each 
other  unchanged  by  merely  altering  the  temperature  a  few 
degrees.  Many  other  substances  besides  water  dissolve 
bodies  without  acting  chemically  on  them.  Spirit  of  wine 


58  Hydrogen. 

dissolves  camphor,  coal  naphtha  dissolves  caoutchouc, 
and  each  is  left  unchanged  when  the  spirit  or  the  naphtha 
evaporates. 

In  a  case  of  true  chemical  action,  the  result  is  different ; 
the  product  obtained  differs  in  properties  from  the  original 
bodies.  When  potassium  is  thrown  into  water,  the  metal 
disappears,  and  seems  to  dissolve,  but  it  cannot  be  removed 
by  evaporation.  The  water  has  been  decomposed,  hydrogen 
escapes,  and  on  evaporation  a  solid  compound  of  potassium 
and  hydrogen  with  oxygen,  in  perfectly  definite  proportions, 
is  obtained  (KHO),  and  this  may  be  made  red  hot  without 
being  chemically  altered. 

(16)  HYDROGEN:  Symb.  H;  Atomic  Wt.  i;  Atomic  Vol. 
Q  ;  MoL  Wt.  H2,  2  ;  MoL  Vol.  fTI ;  $P-  Gr.  0*0691 ;  ReL 
Wt.  i. 

We  have  already  found  that  when  sodium  or  potassium  is 
placed  in  water  an  immediate  escape  of  hydrogen  occurs,  as 
a  colourless  inflammable  gas. 

Potassium  and  sodium  are  among  the  few  bodies  which 
act  powerfully  upon  water  at  common  temperatures  :  there 
are  some  other  metals  which,  when  cold,  have  scarcely  any 
action  upon  it,  though  when  made  red  hot  they  easily 
decompose  it.  Iron  is  one  of  these  metals. 

Exp.  44. — Procure  an  iron  gaspipe  about  60  centim.  long  and 
2  centim.  in  diameter ;  fit  a  cork  and  a  short  piece  of  glass  tube 
to  each  end.  Introduce  some  iron  filings  into  the  iron  tube. 
To  one  end  attach  a  quill  tube  by  means  of  a  flexible  caoutchouc 
tubing ;  and  to  the  other,  also  by  means  of  a  vulcanised  rubber 
tube,  fasten  a  Florence  flask  about  one-third  full  of  water,  fittei 
with  a  cork  and  quill  tube.  Make  a  temporary  furnace  (; 
shown  in  Fig.  13)  by  means  of  six  or  eight  bricks,  with 
grating,  which  may  consist  simply  of  a  coarse  piece  of  wire 
gauze ;  support  the  iron  tube  across  the  furnace,  and  make  it 
red  hot  by  surrounding  it  with  burning  charcoal.  Then  cause 
the  water  in  the  flask  to  boil  with  such  force  as  to  drive  the  steam 


i~i\~ 

3C. 

uc 
>er 

? 

irf» 


Preparation  of  Hydrogen. 


59 


through  the  red-hot  pipe  over  the  heated  iron  filings.     Gas  will 
come  off  at  the  other  end,  and  maybe  collected  in  jars  over  the 

Fig.  13. 


pneumatic  trough.     When  a  light  is  applied  to  it,  it  will  burn 
with  a  pale  yellowish  flame.     It  is,  in  fact,  hydrogen. 

In  this  process  the  red-hot  iron  has  removed  the  oxygen 
from  the  vapour  of  water,  and  left  the  hydrogen  in  a 
separate  form,  magnetic  oxide  of  iron  being  produced.  The 
decomposition  may  be  thus  represented  : 


240 


240 


The  usual  and  the  most  convenient  mode  of  preparing 
hydrogen  is  the  following  :  — 

Exp.  45.  —  Melt  about  half  a  kilogram  of  zinc  in  an  iron  ladle, 
and  pour  it  in  a  thin  stream  from  a  height  of  about  a  metre  into 
a  pailful  of  cold  water  ;  the  metal  will  be  obtained  in  flakes,  and 
is  said  to  be  granulated.  Introduce  into  a  bottle  which  will  hold 
about  300  c.  c.  about  15  grams  of  granulated  zinc;  fit  a  good 
cork  to  the  neck  of  the  bottle  ;  then  remove  the  cork  and  pierce 
two  holes  in  it  with  a  round  file  ;  through  one  hole  pass  a  glass 
tube  funnel,  and  through  the  other  a  tube  bent  as  in  Fig.  14. 
To  the  bent  tube  attach  another  bent  glass  tube,  by  means  of  a 


6o 


Formation  of  Hydrogen. 


piece  of  vulcanised  rubber  tubing.     Next  pour  upon  the  zinc 
through  the  funnel  about  70  c.  c.  of  diluted  sulphuric  acid  (i  mea- 
Fig.  14.  sure  °f  strong  acid  to  7  measures  of 

water).  A  brisk  effervescence  will 
occur,  and  a  colourless  gas  will  come 
off,  which  may  easily  be  collected  in 
jars  over  the  pneumatic  trough. 

In  this  case  the  zinc  appears  to 
displace  hydrogen  from  the  acid ; 
a  new  salt  (zinc  sulphate)  is  formed, 
and  becomes  dissolved  in  the  water. 
The  reaction  is  shown  in  the  fol- 
lowing equation  : — 

Sulphuric  Acid  Zinc  Zinc  Sulphate  Hydrogen 

HaSO4  +       Zn      -          ZnSO4  +        H4 

2x2  +  32+4x16  65  65  +  32  +  4x16  2X1 

Scraps  of  iron  may  be  used  instead  of  zinc  in  this  experi- 
ment; but  the  gas  then  has  a  disagreeable  smell,  owing 
to  the  presence  of  carburetted  hydrogen  derived  from  the 
carbon  in  the  iron.  Ferrous  sulphate  (FeSO4)  is  now  formed 
instead  of  zinc  sulphate. 

Hydrogen  is  not  a  poison  when  breathed,  but  it  cannot 
support  life.     It  is  very  slightly  soluble  in  water;  100  c. 
of  water  dissolve  only  i  -93  c.  c.  of  the  gas. 

Hydrogen  is  a  colourless  gas ;  when  pure  it  is  without 
either  taste  or  odour.  It  has  never  been  liquefied  by  cold 
or  pressure.  Owing  to  its  lightness  it  was  at  one  time  used 
for  filling  balloons ;  but  coal  gas  is  now  substituted  for  it,  as, 
though  not  so  light  as  hydrogen,  it  is  more  easily  obtained 
in  sufficient  quantity. 

Exp.  46. — Hold  a  small  jar,  with  its  mouth  downwards,  over 
the  tube  of  the  hydrogen  bottle  while  it  is  giving  off  gas  freely, 
as  shown  in  Fig.  1 5.  The  hydrogen  will  gradually  displace  the 
heavier  air,  and  may  be  found  in  the  jar  even  after  the  lapse  of 
two  or  three  minutes,  if  the  mouth  of  the  jar  be  kept  downwards, 


Properties  of  Hydrogen. 


61 


as  may  be  proved  by  applying  a  flame,  when  it  will  take  fire ;  but 
if  the  mouth  be  turned  upwards,  the  gas  will  escape  in  a  few 


Fig.  15. 


seconds,  and  no  flash  will  occur 
on  applying  a  light. 

Hydrogen  in  burning  gives 
out  little  light,  but  much 
heat ;  a  jet  of  the  gas  burns 
with  a  pale  yellowish  flame. 

All  gases  which  are  formed 
in  contact  with  water  neces- 
sarily contain  a  certain  small 
amount  of  moisture  in  the 
invisible  form ;  but  they  may 
be  freed  from  this  whenneces- 
sary  by  causing  the  gas  to  pass 
slowly  over  some  salt,  which, 
like  calcic  chloride,  has  a 
strong  attraction  for  moisture. 
For  the  purpose  of  removing  this  small  quantity  of  moisture 
from  hydrogen,  as  ordinarily  prepared,  the  following  arrange- 
ment may  be  made  : — 

Exp.  47. — Fill  a  tube  of  about  20  centim.  long  with  calcic 
chloride  broken  into  pieces  about  the  size  of  a  pea ;  plug  each 
end  loosely  with  cotton  wool;  then  fit  a  cork,  pierced  with  a 
quill  tube  5  centim.  long,  into  each  end ;  fasten  this  drying  ap- 
paratus to  the  hydrogen  bottle  by  means  of  the  caoutchouc  tube. 
The  gas  as  it  comes  out  at  the  other  end  of  the  drying  tube  will 
be  dry.  Now  set  fire  to  the  dry  gas  as  it  escapes,  and  hold 
a  cold  glass  jar  over  the  burning  jet.  The  side  of  the  glass 
will  quickly  become  bedewed  with  moisture,  owing  to  the  union 
of  the  burning  hydrogen  with  oxygen  obtained  from  the  atmo- 
sphere. 

Oxygen  and  hydrogen  may  be  kept  mixed  together  at 
ordinary  temperatures  for  any  length  of  time  without  com- 
bining ;  but  if  an  electric  spark  be  applied  to  the  mixture, 
or  a  lighted  or  even  a  glowing  match,  immediate  combination 
occurs,  with  a  bright  flash  and  a  loud  report. 


02 


The  Mixed  Gases. 


Exp.  48. — Fit  a  good  cork  into  the  neck  of  a  gas  jar,  and 
pass  a  quill  tube  5  centim.  long  through  it.  Bind  a  short  piece 
of  caoutchouc  tube  firmly  to  the  quill  tube,  and  close  this  elastic 
tube  with  a  small  screw  vice  or  tap  made  for  such  purposes. 
Fill  the  jar  with  water  over  the  pneumatic  trough.  Now  fill  a 
small  jar  which  will  hold  about  half  a  litre  with  oxygen,  and 
transfer  it  by  manipulating,  as  shown  in  Fig.  16,  without  loss  to 
the  gas  jar.  Fill  the  same  jar  with  hydrogen,  and  transfer 
^__it  to  the  large  jar.  Repeat  the  operation  with  the  hydrogen,  so 
as  to  obtain  in  the  larger  jar  a  mixture  of  half  a  litre  of  oxygen 

Fig.  1 6. 


and  i  litre  of  hydrogen.  Having  previously  softened  a  thin 
bladder  by  soaking  it  in  water,  tie  into  the  neck  of  it  a  glass 
quill  tube  5  centim.  long  :  then  adjust  to  the  projecting  portion 
a  piece  of  vulcanised  caoutchouc  tubing  provided  with  another 
screw  tap.  Press  the  air  out  of  the  bladder  ;  connect  by  means 
of  a  short  piece  of  glass  tubing  the  two  pieces  of  vulcanised 
tube ;  depress  the  jar  in  the  pneumatic  trough,  and  then  open 
each  screw  tap.  The  gas  will  now  pass  into  the  bladder  ;  close 
both  screw  taps,  and  remove  the  bladder.  Now  place  the  end 
of  the  tube  attached  to  the  bladder  under  some  soapsuds,  and 


Union  of  Hydrogen  and  Oxygen.  63 

force  out  the  mixed  gas  by  squeezing  the  bladder  so  as  to  make 
a  lather.  Carefully  remove  the  bladder  to  a  distance,  and  then 
apply  a  light  to  the  froth  of  soapsuds.  A  loud  explosion  will 
immediately  follow. 

In  this  experiment  steam  is  formed ;  this  first  expands  con- 
siderably, owing  to  the  heat  produced  by  the  combination  of 
the  oxygen  and  hydrogen,  and  immediately  afterwards  the 
steam  becomes  condensed,  the  particles  of  the  surrounding 
air  rush  in  to  fill  the  void,  and  by  striking  one  against  the 
other  produce  the  report. 

If  the  hydrogen  be  mixed  with  air,  instead  of  pure  oxygen, 
a  similar  but  weaker  explosion  occurs  when  a  light  is  applied. 
In  all  experiments  with  hydrogen  it  is  therefore  necessary 
to  allow  time  for  the  expulsion  of  the  air  from  the  apparatus 
before  setting  fire  to  the  gas  as  it  comes  out.  If  the  mixture 
be  diluted  with  a  large  excess  of  hydrogen  or  of  air,  the 
explosion  becomes  less  sudden,  and  less  heat  is  given  out ; 
until,  when  the  dilution  reaches  a  certain  point,  the  mixture 
only  burns  quickly  without  explosion,  and,  if  still  more 
diluted,  the  combustion  only  takes  place  at  the  spot  where 
heat  is  applied. 

The  proportion  of  oxygen  and  hydrogen  which  unite 
together  is  perfectly  defined,  no  matter  in  what  proportion 
they  are  mixed.  One  measure  of  oxygen  invariably  unites 
with  exactly  two  measures  of  hydrogen.  If  the  gases  before 
firing  are  heated  beyond  the  temperature  of  boiling  water, 
and  be  kept  at  the  same  temperature  after  the  explosion,* 
the  three  measures  of  gas  which  have  united  will  form  exactly 
two  measures  of  steam — 

|H|H|  +  [o]    =    [ajol. 

It  might  be  considered  that  we  now  have  proved  the  true 
composition  of  water,  for  we  have  found  that  water  may 
by  analysis  be  made  to  yield  both  oxygen  and  hydrogen,  and 

*  This  form  qf  the  experiment  requires  special  apparatus,  and,  except 
in  practised  hands,  is  rather  difficult  of  performance 


64 


Composition  of  Water. 


Fig.  17. 


that  when  oxygen  and  hydrogen  are  burned  water  is  formed  ; 
but  at  present  we  have  not  shown  absolutely  that  oxygen  and 

hydrogen  are  the  only  sub- 
stances which  enter  into  the 
formation  of  water. 

The  following  mode  of  ex- 
A  1 '!    I  periment,  for  which  a  some- 

what costly  form  of  apparatus 
is  required,  proves  this  fact, 
>  C  however,     in     a    conclusive 

manner. 

Exp.  49.  —  Fig.  17  repre- 
sents a  strong  glass  vessel  A, 
through  the  upper  part  of 
which  two  platinum  wires  are 
inserted;  the  vessel  can  be 
closed  by  a  glass  stop-cock  c  ; 
by  means  of  a  second  stop- 
cock it  can  be  attached  to  an 
air-pump,  not  shown  in  the 
figure,  and  the  air  exhausted. 
The  stop-cocks  having  been 
closed,  the  vessel  is  screwed  upon  the  top  of  a  jar,  B,  containing  a 
mixture  of  two  measures  of  hydrogen  and  one  measure  of  oxygen. 
On  opening  the  stop-cocks  a  portion  of  the  mixture  enters  the 
vessel ;  the  cocks  are  then  closed,  and  an  electric  spark  passed 
through  the  mixture.  A  bright  flash  occurs;  the  gases  com- 
bine, and  the  whole  of  the  two  gases  become  condensed  into 
water,  which  trickles  down  the  sides  of  the  glass.  On  again 
opening  the  stop-cocks  a  fresh  quantity  of  gases  may  be  ad- 
mitted, to  supply  the  place  of  those  just  condensed.  The  spark 
may  be  again  transmitted,  and  the  process  may  be  repeated 
until  the  whole  of  the  gases  are  consumed  and  a  considerable 
quantity  of  water  formed. 

If  in  this  experiment  oxygen  or  hydrogen  be  used  in  ex- 
cess, that  excess  will  be  found  in  the  vessel  unacted  on  after 
firing  the  mixture. 


Fig.  18. 


Synthesis  of  Water.  65 

Exp.  50. Provide  a  stout  tube  bent  into  the  form  shown  in 

Fig.  1 8,  open  at  one  end  and  sealed  at  the  other,  the  sealed 
limb  having  been  divided  into  cubic  centimetres,  or  other  equal 
divisions.     Into  the  sides  of  the  tube,  near  the  sealed  extremity, 
two  platinum  wires  are  fused,  with  two  of  the  ends  inside  the 
tube,  nearly  touching  each  other.     Fill  the  tube  with  mercury ; 
then  introduce  a  mixture  of  4  volumes  of  oxygen  and  2  volume? 
of  hydrogen.     The  bulk  of  this  gas 
is  to  be  carefully  measured ;  say  it 
fills  6  divisions  after   causing  the 
liquid  metal  to  stand  at  the  same 
level  in  both  tubes;  this  may  be 
easily  effected  either  by  adding  mer- 
cury or  by  drawing  it  off  through 
the  caoutchouc  tube  and  screw-tap 
near  the  bottom.     The  open  end  of 
the  tube  must  now  be  firmly  closed 
with  a  cork,  below  which  a  column 
of  air  is  included.  This  air  is  meant 
to   act  as    a  spring  for  gradually 
checking  the  force  of  the  explosion, 
which  is   now  to  be  produced  by 
passing  an  electric  spark  either  from 
a  Leyden  jar  or  an  induction  coil 
between  the  wires.     After  the   ex- 
plosion the  gas  in  the  closed  limb 
will  measure  less  than  before.  With- 
draw the  cork,  and  add  mercury  until  the  metal  again  stands  at 
the  same  height  in  both  tubes.    Suppose  the  gas  filled  6  divisions 
before  the  spark  was  passed ;  it  fills  just  3  divisions  afterwards  : 
the  2  volumes  of  hydrogen  which  the  mixture  contained  combine 
with  i  volume  of  oxygen,  and  immediately  condense  into  mois- 
ture on  the  cold  sides  of  the  tube.    The  remaining  3  volumes  may 
be  shown  to  be  oxygen  as  follows  : — Fill  up  the  open  limb  with 
mercury;  close  it  with  the  thumb  ;  then  incline  the  tube  so  as 
to  transfer  the  gas  from  the  sealed  to  the  open  limb.     A  match 
with  a  red-hot  point  will  immediately  blaze  up  if  introduced  into 
it  (Exp.  7). 

Such  an  instrument  (Fig.  18)  is  called  a  eudiometer,  and 
is  often  used  for  the  analysis  of  mixtures  of  gases. 


66 


Synthesis  of  Water. 


Pure  water  may  also  be  formed  in  considerable  quantities 
by  the  following  method,  which  rests  on  this  important  fact, 
that  when  cupric  oxide  is  heated  in  contact  with  hydrogen, 
it  gives  up  its  oxygen  to  the  hydrogen,  and  the  two  unite  to 
form  water,  which  may  not  only  be  collected  and  weighed, 
but  the  proportion  by  weight  of  each  of  its  constituents  may 
also  be  determined. 

Exp.  51. — Place  a  quantity  of  pure  and  dry  cupric  oxide 
(CuO)  in  a  globe,  F  (Fig.  19),  made  of  glass  of  difficult  fusibility, 
and  weigh  the  globe  and  its  contents  accurately.  Hydrogen  is 
next  to  be  disengaged  steadily,  by  adding  small  quantities  of 


Fig.  19. 


diluted  sulphuric  acid  to  granulated  zinc  contained  in  the  bottle 
A.  Let  the  gas  bubble  up  through  a  solution  of  potash  in  B,  and 
then  pass  through  the  tube  c,  which  is  rilled  with  fragments  of 
pumice  moistened  with  a  solution  of  corrosive  sublimate  (HgCl2), 
then  through  D,  which  is  rilled  with  pieces  of  fused  potash,  and 
lastly  through  E,  which  contains  fragments  of  pumice  moistened 
with  strong  sulphuric  acid.  The  potash  and  the  mercuric  salt 
remove  traces  of  arsenicum,  sulphur,  and  carburetted  compounds 
derived  from  impurities  in  the  acid  or  the  zinc,  while  the  tube  E 
deprives  the  gas  of  every  trace  of  moisture.  In  this  way  pure 
and  dry  hydrogen  is  obtained  before  it  passes  into  the  globe  F. 
When  all  the  air  of  the  apparatus  has  been  displaced,  by  allow- 
ing a  certain  quantity  of  hydrogen  to  pass  through  it  to  waste, 


The  Oxy-hydtogen  Jet. 


Fig.  20 


heat  is  applied  to  the  globe  F.  The  cupric  oxide  when  heated 
alone  is  not  altered,  but  when  heated  with  hydrogen  it  loses 
oxygen,  which  converts  the  hydrogen  into  water ;  this  is  collected 
in  the  receiver  G  and  the  bent  tube  H,  which  contains  pieces  of 
pumice  moistened  with  strong  sulphuric  acid.  When  the  globe  F 
is  cold,  pass  a  current  of  air  through  the  apparatus,  for  the 
purpose  of  displacing  the  hydrogen  left  in  it.  Weigh  the 
globe  with  the  oxide  a  second  time  :  the  loss  shows  how  much 
oxygen  has  been  removed.  Weigh  also  the  receivers  G  and  H 
again :  the  increase  in  weight  shows  how  much  water  has  been 
condensed;  the  difference  between  the  oxygen  lost  by  F  and  the 
water  gained  by  G  and  H  is  the  hydrogen  which  has  combined 
with  the  oxygen  to  form  water. 

By  numerous  careful  experiments 
performed  in  this  way  it  has  been  found 
that  1 6  grams  of  oxygen  combine  with 
exactly  2  grams  of  hydrogen  to  form 
1 8  grams  of  water. 

Hydrogen,  in  combining  with  oxy- 
gen, gives  out  a  heat  surpassing  that 
which  any  other  chemical  action  pro- 
duces. By  forcing  a  jet  of  oxygen 
through  the  flame  of  a  spirit  lamp,  of 
coal  gas,  or  of  hydrogen,  a  very  high 
temperature  is  immediately  obtained ; 
but  the  most  intense  heat  is  procured 
by  sending  a  jet  of  oxygen  into  the 
midst  of  a  jet  of  hydrogen  by  means 
of  two  concentric  tubes,  as  shown  in 
Fig.  20.  The  outer  tube,  provided  with 
the  stop-cock  H,  is  connected  with  a 
large  bladder  or  bag  of  hydrogen,  placed 
under  a  weighted  board,  which  by  its 
pressure  drives  out  the  gas,  while  the 
inner  tube,  with  its  stop- cock  o,  is  connected  with  another 
bag,  which  supplies  oxygen.  If  the  mixed  gas,  as  it  issues, 
is  kindled,  a  small  feebly  luminous  but  intensely  hot  jet  of 


68  Synthesis  of  Water. 

flame  is  obtained,  in  which  a  thick  platinum  wire  may  be 
quickly  melted  and  partially  volatilised.  Thick  iron  and  steel 
wires  held  in  this  flame  are  also  easily  melted,  and  burn, 
giving  off  brilliant  sparks.  Rock  crystal  melts  in  it  like 
glass,  and  the  stem  of  a  tobacco  pipe  fuses  without  difficulty. 
If  the  jet  be  directed  on  a  pellet  of  lime,  the  earth  does  not 
fuse,  but  becomes  white  hot,  giving  out  a  very  pure  white 
light,  which,  under  the  name  of  the  '  Drummond  light,' 
has  been  extensively  used  for  signalling,  and,  when  pro- 
perly mounted  in  the  focus  of  a  concave  mirror,  has  been 
seen,  from  great  elevations,  at  a  distance  of  more  than 
TOO  miles. 

The  combustion  of  the  mixed  gases,  as  the  oxygen  and 
hydrogen  in  proper  proportions  are  termed,  produces,  as  we 
know,  pure  water.  Water  is  also  formed  abundantly  when- 
ever combustible  bodies  which  contain  much  hydrogen  are 
burned  in  the  open  air;  such,  for  instance,  as  wood,  oil, 
tallow,  spirit  of  wine,  and  coal  gas.  A  tallow  candle,  in 
burning,  produces  rather  more  than  its  own  weight  of 
water;  and  alcohol  or  spirit  of  wine  yields  a  still  larger 
amount. 

Exp.  52. — Hold  a  cold  glass  over  a  burning  candle  :  it  will 
quickly  become  bedewed  with  moisture. 

A  similar  result  may  be  observed  every  time  a  retort  or 
vessel  containing  cold  liquid  is  heated  over  the  flame  of  a 
lamp  or  of -gas  :  drops  of  water  condense  until  the  vessel 
becomes  sufficiently  hot  to  prevent  this  effect  from  oc- 
curring. 

Hydrogen  is  rapidly  absorbed  by  many  porous  bodies, 
particularly  by  the  metals  platinum  and  palladium.  Palla- 
dium, indeed,  can  absorb  as  much  as  900  times  its  bulk  < 
hydrogen  gas  without  losing  its  brilliant  lustre.  It  retains 
the  gas  at  ordinary  temperatures,  but  loses  it  by  degrees  if 
the  temperature  be  raised ;  and  if  heated  to  redness,  in  a 
vessel  from  which  the  air  is  exhausted,  all  the  hydrogen  may 
be  again  extracted. 


Diffusion  of  Hydrogen.  69 

Exp.  53. — Fasten  a  piece  of  spongy  platinum  (a  form  in  which 
the  metal  may  be  obtained  by  heating  its  compound  chloride 
[2H4NC1,  PtCl4],  as  wiU  be  explained  hereafter)  to  a  thin  pla- 
tinum wire,  and  hold  it  in  a  jet  of  hydrogen  as  it  escapes  into  the 
air.  The  cold  platinum  will  become  red  hot,  and  kindle  the  gas. 

This  effect  appears  to  be  due  to  the  condensation  of  the 
gas  by  the  platinum,  which  also  condenses  oxygen  from  the 
air,  and  the  heat  attending  the  condensation  is  sufficient 
ultimately  to  set  fire  to  the  mixture  of  gases. 

Another  peculiar  property  of  gases  is  well  exhibited  by 
hydrogen.  Whenever  two  gases  are  placed  in  vessels  which 
communicate  with  each  other,  the  gases  become  gradually 
intermingled,  although  they  may  not  have  any  tendency  to 
chemical  combination;  and  the  greater  the  difference  in 
density  between  them,  the  more  rapidly  does  this  process  of 
diffusion,  as  it  is  called,  take  place. 

Exp.  54. — Take  a  tube  of  about  20  centim.  long  and  2  centim. 
wide,  open  at  both  ends.  Mix  a  little  plaster  of  Paris  with 
water  so  as  to  be  of  the  consistence  of  thick  cream,  and  im- 
merse one  end  of  the  glass  tube  in  the  mixture  to  the  depth  of 
5  mm.  In  about  ten  minutes  the  plaster  will  have  become 
solid,  and  on  raising  the  tube  out  of  the  mixture  its  extremity 
will  be  closed  with  a  thin  plate  of  plaster ;  let  it  dry  in  a  warm 
room  for  a  couple  of  days.  Through  this 
porous  plug  the  effects  of  diffusion  may 
be  observed.  Fill  this  diffusion-tiibe  with 
hydrogen  gas  by  displacement,  covering 
the  plug  of  plaster  with  a  cap  of  tinfoil 
when  the  tube  is  full  of  hydrogen.  Place 
it  in  a  tall  jar  of  water  (Fig.  21),  with  the 
open  end  downwards,  and  remove  the 
tinfoil.  The  water  will  rise  rapidly  in  the 
tube,  as  though  it  were  dissolving  the  gas, 
and  will  soon  fill  it  above  two-thirds  of  its  height. 

In  this  experiment  the  porous  plug  favours  the  diffusion 
of  the  hydrogen  :  about  3-8  measures  of  hydrogen  pass  out, 
while  only  i  measure  of  air  enters ;  hence  the  liquid  rises  in 
the  tube.  (See  Appendix.) 


7O  Hydrogen  the  Unit. 

Other  gases  exhibit  a  similar  tendency  to  diffusion,  though 
to  a  less  extent,  the  diffusiveness  depending  upon  the  relative 
density  of  the  two.  Its  amount  admits  of  exact  calculation, 
supposing  the  specific  gravity  of  the  gas  to  be  known.  The 
rule  is  to  take  the  square  root  of  the  number  which  re- 
presents the  specific  gravity  of  the  gas,  and  divide  i  by 
this  number :  the  fraction  thus  obtained  is  the  diffusiveness 
required. 

For  example,  the  numbers  which  represent  the  specific 
gravity  of  oxygen  and  hydrogen,  1*1057  and  0*0691,  are  to 
each  other  in  the  proportion  of  1 6  to  i.  The  square  root 
of  1 6  is  4,  and  the  square  root  of  i  is  i.  Now,  the  rate 
at  which  hydrogen  diffuses  into  an  atmosphere  consisting 
of  pure  oxygen  is  as  4  to  i.  That  is  to  say,  that  when  proper 
precaution  is  used  in  making  the  experiment  with  such  a 
diffusion-tube  as  that  described,  while  4  measures  of  hydro- 
gen pass  out  into  the  oxygen  through  the  plaster,  i  measure 
of  oxygen  would  pass  into  the  hydrogen  in  the  opposite 
direction.  The  specific  gravities  of  air  and  hydrogen  are 

i  and  0*0691,  and  their  rates  of  diffusion  are  — —  (=  i)  and 

.  _  -,  or  i  and  3*8.  In  fact,  3*8  measures  of  hydrogen 
v  0*0691 

become  diffused  into  the  air,  while  i  measure  of  air  is  being 
diffused  at  the  same  time  into  the  hydrogen. 

Hydrogen  is  the  lightest  substance  known ;  an  equal  bulk 
of  oxygen  being  16  times  as  heavy,  and  an  equal  bulk  of 
air  14*47  times  as  heavy  as  the  same  bulk  of  hydrogen  under 
similar  circumstances  of  temperature  and  pressure.  Hydro- 
gen has  also  a  smaller  combining  number  than  any  other 
elementary  body ;  and  this,  with  its  lightness,  furnish  two  of 
the  reasons  which  have  induced  chemists  to  take  hydrogen 
as  the  unit  or  standard  of  comparison  both  for  atomic 
weights  and  combining  volumes.  The  atomic  weight  of 
hydrogen  has  been  therefore  taken  as  i,  or  H  =  i,  and  its 
combining  volume  is  also  i,  or  H  =  |  |. 


Hydrogen  and  Chlorine,  Oxygen,  &c.  7 1 

Suppose,  then,  i  gram  of  hydrogen  to  be  the  unit  of 
weight,  the  space  it  would  occupy  at  o°,  under  a  barometric 
pressure  of  760  mm.,  would  be  11*19  litres.  The  same 
volume  of  oxygen  would  weigh  16  grams,  of  nitrogen 
14  grams,  of  chlorine  35*5  grams.  This  volume,  11*19  litres, 
may,  therefore,  be  regarded  as  representing  i  gas  volume. 
For  many  purposes,  however,  the  litre  is  a  convenient  mea- 
sure ;  and  i  litre  of  hydrogen,  at  the  temperature  of  o°  and 
760  mm.  pressure,  weighs  89*6  milligrams. 

The  proportion  in  volume  in  which  a  certain  fixed  volume 
of  each  of  the  elementary  gases  or  vapours  combines  with 
hydrogen,  and  the  volume  of  gas  or  vapour  which  such 
combinations  furnish,  compared  with  the  space  they  occupy 
before  combination,  affords  a  character  upon  which  the 
grouping  of  the  different  elements  into  natural  families  is 
founded. 

For  example,  when  a  litre  of  chlorine  unites  with  hydrogen, 
it  does  so  in  the  proportion  of  i  litre  of  hydrogen,  and  it 
forms  with  it  2  litres  of  a  new  compound,  hydrochloric  acid 
gas;  but  a  litre  of  oxygen,  when  it  unites  with  hydrogen, 
requires  not  less  than  2  litres  of  hydrogen,  though  it  still 
forms  only  2  litres  of  the  new  body,  aqueous  vapour ;  further, 
if  a  litre  of  nitrogen  be  combined  with  hydrogen,  it  will  unite 
with  3  litres  of  hydrogen,  and  yet  will  form  only  2  litres  of 
the  resulting  ammoniacal  gas.  Consequently,  if  the  hydro- 
chloric acid  be  represented  by  the  symbols  HC1,  it  is  agreed 
by  chemists  to  represent  the  equal  bulk  of  aqueous  vapour  as 
H2O,  and  the  same  bulk  of  ammonia  as  H3N. 

We  see,  then,  that  a  single  volume  of  chlorine,  of  oxygen, 
and  of  nitrogen,  when  uniting  severally  with  hydrogen, 
requires,  respectively,  one,  two,  and  three  volumes  of  hydro- 
gen, while  in  every  one  of  these  cases  the  compound  which 
is  formed  measures  two  volumes,  no  matter  whether  the 
volume  used  be  a  cubic  centimetre,  a  litre,  a  cubic  inch,  a 
cubic  foot,  or  any  other  volume  which  may  be  agreed  on. 

Further,  it  is  important  to  remember  that  the  quantity  of 


72  Monad,  Dyad,  &c.  Elements. 

any  compound  represented  by  its  formula  is  spoken  of  as  its 
molecule ;  and  when  the  body  is  known  in  the  aeriform  state, 
that  molecule  is  always  tacitly  compared  with  an  equal 
bulk  of  hydrogen,  which  is  represented  by  the  formula  H2  ; 
and  this  amount  of  hydrogen  is  also  spoken  of  as  its 
molecule.* 

In  the  table  which  follows,  some  of  the  most  important 
gaseous  compounds  of  the  different  elements  are  enumerated. 
In  each  case  the  quantity  represented  by  the  formula  indi- 
cates 2  volumes,  say  2  litres,  of  the  gaseous  compound. 
H  =  i,  being  £]  i  volume  or  i  litre,  and  H2  =  2  volumes 

~]  or  2  litres. 

In  the  first  column  all  the  compounds  are  represented  m 
their  formulae  as  furnished  by  the  union  of  single  volumes 
of  each  element,  the  two  bodies  combining  volume  to  volume. 
Elements  which  combine  in  this  way  are  called  monads,  or 
univalent  elements. 

In  the  second  column  two  volumes  of  hydrogen  are  repre- 
sented in  combination  with  a  single  volume  of  certain  other 
elements,  which,  from  their  power  of  chemically  uniting  witli 
two  volumes  of  hydrogen,  have  been  termed  dyads,  or  bi- 
valent elements. 

In  the  third  column  each  of  the  compounds  contains  3 
volumes  of  hydrogen  united  with  i  volume  of  one  of  the 
elements  of  a  natural  group  known  as  the  triads,  or,  as  they 
are  sometimes  called,  tervalent  elements,  f  i  volume  of  each 
of  these  element  requiring  3  volumes  of  hydrogen  to  form 
the  compound. 

And,  lastly,  in  the  fourth  column  the  compounds  repre- 
sented each  contains  4  volumes  of  hydrogen,  united  with  a 
fixed  quantity  of  certain  elements,  which  cannot  be  obtained 

*  Some  further  observations  on  gaseous  molecules  will  be  found  in 
the  paragraph  on  the  atomic  theory. 

t  Phosphorus  and  arsenicum  are,  however,  exceptional,  since  they 
combine  with  3  volumes  of  hydrogen  in  the  proportion  of  J  a  volume 
of  their  vapour. 


Monads,  Dyads,  Triads,  &c. 


73 


separately  as  gases,  but  which  are  distinguished  as  tetrads, 
or  quadrivalent  elements.* 


COMPOUNDS  OF 
MONADS 

COMPOUNDS  OF 
DYADS 

COMPOUNDS  OF 
TRIADS 

COMPOUNDS  OF 
TETRADS 

Hydrochloric 
Acid 

HC1 

Water 

HaO 

Ammonia 

H3N 

Marsh  Gas 

H4C 

Hydrobromic 
Acid 

HBr 

Sulphuretted 
Hydrogen 

HaS 

Phosphuretted 
Hydrogen 

sJSC 

Siliciuretted 
Hydrogen 

H4Si 

Hydriodic 
Acid 

HI 

Seleniuretted 
Hydrogen 

H,Se 

Arseniuretted 
Hydrogen 

H3As 

Hydrofluoric 

Acid 

HF 

Telluretted 
Hydrogen 

H2Te 

Antimoniuretted 
Hydrogen 

H3Sb 

The  compounds  which  hydrogen   forms  when  it  unites 
with  any  other  elementary  body  are  known  as  hydrides. 


CHAPTER  IV. 

OXIDES    OF   CARBON — CARBON. 

(17)  CARBONIC  ANHYDRIDE  (Carbon  Dioxide,  or  Car- 
bonic Acid] :  Symbol,  CO2  ;  Atomic  Weight,  44 ;  Atomic 
and  Molecular  Volume,^  "^  •  Specific  Gravity,  1*529;  Re- 
lative Weight,  22. 

We  have  already  seen  that  when  a  saucer  containing 
limewater  is  exposed  to  the  air  for  a  few  minutes,  the  surface 
of  the  limewater  becomes  covered  with  a  thin  insoluble  crust 

*  The  elements  which  combine  with  I,  with  3,  or  with  an  uneven 
number  of  volumes  of  hydrogen  are  sometimes  further  distinguished  as 
perissad  elements  ;  and  those  which  combine  with  2,  4,  or  an  even 
number  of  volumes  of  hydrogen  are  called  artiad  elements. 


74  Formation  of  Carbonic  Anhydride. 

or  pellicle,  consisting  of  chalk,  which  is  formed  by  the  union 
of  carbonic  anhydride  contained  in  the  atmosphere  with  the 
lime,  CO2  +  CaO  forming  CaCO3.  Such  compounds  of 
carbonic  anhydride  with  bases  are  called  carbonates  ;  hence 
chalk  is  called  calcic  carbonate,  or  often  carbonate  of  lime. 
When  chalk  is  heated  to  bright  redness,  the  carbonic  anhy- 
dride is  driven  off,  and  the  lime  is  left  behind,  as  in  the 
ordinary  process  of  burning  limestone  into  lime,  CaCO3 
becoming  separated  into  CaO  and  CO2. 

The  carbonic  is  a  very  weak  acid,  and  may  be  displaced 
from  its  compounds  by  almost  every  acid  which  is  soluble 
in  water. 

Exp.  55. — In  a  glass  bottle,  similar  to  that  used  for  preparing 
hydrogen  (Fig.  14),  place  15  or  20  grams  of  chalk  in  small 
lumps,  or  of  marble,  which  is  a  crystalline  form  of  the  same 
chemical  compound.  Pour  on  it  some  strong  acid,  such  as  the 
hydrochloric  (muriatic),  HC1,  diluted  with  8  or  10  times  its  bulk 
of  water. 

In  this  experiment  the  acid  exchanges  its  hydrogen  for 
the  calcium,  producing  calcic  chloride  (CaCl2)  on  the  one 
hand,  and  carbonic  acid  (H2CO3)  on  the  other.  But  the 
carbonic  acid  is  so  unstable  that  it  immediately  becomes 
decomposed  into  water,  which  remains  behind,  and  into 
carbonic  anhydride,1*  which  comes  off  as  a  gas  with  brisk 
effervescence.  The  decomposition  may  be  represented  as 
follows  : — 

CaC03  +   2HC1     =     CaCl2  +   H2O  +   CO2. 

Limestone  (CaCO3),  pearlash  (K2CO3),  sodic  carbonate 
(Na2CO3),  and  indeed  all  the  carbonates,  may  be  made  to 

*  An  anhydride  is  an  oxide  which,  when  dissolved  in  water,  furnishes 
an  acid,  by  uniting  with  the  elements  of  water ;  and  it  must  be  dis- 
tinguished from  a  true  acid,  which  is  always  a  salt  of  hydrogen.  Some 
writers  are  not  sufficiently  careful  to  distinguish  the  two  classes  of  bodies 
from  each  other.  The  gas  CO2  was  formerly  known  as  carbonic  acid  ; 
but  as  it  is  not  a  salt  of  hydrogen,  it  has  been  found  necessary  to  change 
its  name  for  the  sake  of  precision,  and  it  is  now  called  carbonic  anhy- 
dride, and  sometimes  carbon  dioxide. 


Properties  of  Carbonic  Anhydride.  75 

furnish  carbonic  anhydride  as  easily  as  marble,  when  treated 
with  a  strong  acid. 

Although  carbonic  anhydride  is  usually  obtained  as  a 
heavy  transparent  gas,  without  colour,  and  with  a  faintly 
acidulous  taste  and  smell,  it  can  be  procured  as  a  colourless 
transparent  liquid,  by  generating  it  from  materials  packed 
into  a  small  space  in  a  strong  closed  tube ;  but  it  requires  a 
pressure  of  40  or  50  atmospheres  to  effect  this  ;  and  it  is  not 
an  experiment  that  can  be  made  with  safety  by  an  inex- 
perienced person.  The  gas  is  sometimes  liquefied  in  large 
quantities  for  experimental  purposes  in  strong  wrought-iron 
vessels  constructed  with  this  object.  When  a  stream  of  the 
liquid  thus  obtained  is  allowed  to  escape  into  the  air,  one 
portion  of  the  liquid  evaporates  so  rapidly  as  to  carry  off 
heat  so  quickly  that  it  freezes  the  rest  into  a  snow-white 
solid.  If  this  be  collected  and  mixed  with  ether,  it  produces 
a  cold  bath  or  freezing  mixture  of  great  intensity,  owing  to 
the  rapid  evaporation  of  the  frozen  gas,  which  carries  off 
heat  in  large  quantity  from  any  substance  nearest  to  it ;  a 
cold  estimated  at  —75°  is  thus  easily  attained. 

Exp.  56. — Fill  three  or  four  small  jars  with  the  gas  as  obtained 
in  Exp.  55.  Plunge  a  lighted  candle  into  one  of  them  :  the  flame 
is  extinguished,  but  the  gas  does  not  take  fire. 

It  will  be  remembered  that  other  gases,  such  as  nitrogen, 
put  out  the  light. 

Exp-  57- — Into  another  jar  of  the  gas  pour  two  or  three  table- 
spoonfuls  of  limewater.  It  will  at  once  become  milky,  owing  to 
the  formation  of  chalk ;  two  or  three  drops  of  any  strong  acid 
will  immediately  redissolve  the  chalk. 

This  action  of  the  gas  upon  limewater  is  a  very  con- 
venient and  characteristic  test  of  its  presence,  even  when  it 
is  mixed  largely  with  air  or  other  gases,  since  these  gases  do 
not  render  limewater  turbid. 

Undiluted  carbonic  anhydride  cannot  be  breathed,  be- 
cause the  glottis,  or  valve  at  the  entrance  of  the  windpipe,' 
closes  and  prevents  it  from  entering  the  lungs  ;  but  if  the 


76 


Density  of  Carbonic  A  nhydride. 


Fig.  22. 


gas  be  largely  mixed  with  air ;  that  is,  if  it  be  present  in  a 
quantity  varying  from  3  to  4  per  cent,  of  the  respired  air,  it 
acts  as  a  stupefying  or  narcotic  poison,  by  preventing  the 
proper  action  of  the  air  upon  the  blood  as  it  passes  through 
the  lungs,  and  in  this  way  produces  death.  Part  of  the 
bad  effect  experienced  after  remaining  in  crowded  and  ill- 
ventilated  rooms  is  owing  to  the  presence  of  unusual  quan- 
tities of  this  gas,  the  true  prevention  in  such  cases  being 
efficient  ventilation. 

Carbonic  anhydride  is  more  than  half  as  heavy  again  as 
air.     It  is  just  22  times   as   heavy  as   hydrogen,    so   that 
11*19  litres,  at  o°  C.  and  760  mm. 
bar.,  weigh  22  grams,  while  the  same 
volume  of  air  weighs  only  14*47. 

Exp.  58. — Allow  the  gas  to  pass  to 
the  bottom  of  a  small  jar,  arranged  as 
in  Fig.  22 ;  when  full,  the  gas,  though 
invisible,  may  be  shown  to  be  there,  as 
it  will  extinguish  a  candle  lowered  into 
it  on  a  wire. 

Exp.  59. — Take  a  second  similar  jar 
full  of  air,  and  pour  the  gas  slowly  into 
it  from  the  jar  rilled  as  in  Exp.  58,  as 
though  it  were  water.  The  light  will  now  be  extinguished  if 
lowered  into  the  second  jar,  but  will  burn  if  introduced  into  the 
first. 

Many  amusing  experiments  may  be  made  upon  this 
owing  to  the  ease  with  which,  from  its  density,  it  may 
transferred  from  vessel  to  vessel.     It  may  be  drawn  off  wit 
a  syphon,  ladled  out  with  a  glass,  and  so  on. 

Water  dissolves  about  its  own  bulk  of  carbonic  anhydride 
forming  a  solution  of  carbonic  acid,  CO2  +  H2O  becoming 
H2CO3.  The  water  may  be  made  to  dissolve  considerably 
more  than  its  own  bulk  of  the  gas,  if  it  be  forced  in  unde 
pressure.  It  is  in  this  way  that  the  so-called  soda  water  is 
made,  though  the  water  seldom  contains  soda,  or  inde 


Test  for  Carbonic  Anhydride.  77 

anything  but  the  dissolved  gas.  As  soon  as  the  pressure  is 
removed,  the  gas  escapes  with  effervescence. 

Exp.  60. — Cause  a  stream  of  the  gas  to  bubble  briskly  through 
60  or  100  c.  c.  of  water.  To  a  portion  of  the  solution  of  the  gas 
thus  obtained  add  a  few  drops  of  tincture  of  litmus  :  it  will  be 
reddened.  Now  boil  the  red  liquid  for  a  few  minutes  :  the  gas 
will  be  driven  off  again,  and  the  litmus  will  recover  its  blue 
colour. 

The  solution  of  carbonic  acid  exerts  slight  but  important 
solvent  powers  upon  many  rocks  and  minerals.  This  action 
produces  changes  which,  insignificant  as  the  amount  may 
appear  at  any  given  moment,  yet  in  the  lapse  of  ages  be- 
comes very  considerable,  since  few  natural  waters  are  found 
which  are  not  charged  more  or  less  extensively  with  carbonic 
acid. 

Carbonic  anhydride  is  largely  produced  in  a  variety  of 
important  natural  operations.  Respiration,  or  the  process 
of  breathing,  both  in  man  and  animals,  is  always  attended 
with  the  formation  of  a  large  quantity  of  the  gas. 

Exp.  61. — By  means  of  a  tube  open  at  both  ends  blow  a 
little  air  from  the  lungs  through  limewater ;  it  will  speedily 
become  turbid,  owing  to  the  formation  of  calcic  carbonate. 

Air  which  has  been  breathed  once  contains  from  3^  to  4 
per  cent,  of  the  gas. 

Exp.  62. — Pass  a  little  of  the  air  from  the  lungs,  by  means  of 
a  tube,  into  a  gas  jar  filled  with  water,  and  standing  over  water. 
When  the  water  has  been  displaced  by  the  exhaled  air,  it  may 
be  tried  with  a  lighted  candle,  which  will  quickly  go  out. 

Fermentation  is  another  source  of  carbonic  acid. 

Exp.  63. — Dissolve  15  or  20  grams  of  sugar  in  ten  times  its 
weight  of  water,  at  25°  C.  Add  two  teaspoonfuls  of  brewers' 
yeast,  and  introduce  the  mixture  into  a  Florence  flask  provided 
with  a  cork  and  bent  tube  for  the  escape  of  gas.  In  about  an 
hour's  time  it  will  begin  to  give  off  a  gas  which  puts  out  a  light 
and  makes  limewater  turbid. 

The  briskness  of  bottled  beer  and  of  champagne  is  due  to 


78  Sources  of  Carbonic  Anhydride. 

the  dissolved  carbonic  acid  which  they  contain.  Accidents 
have  often  happened  in  breweries  where  fermentation  is 
carried  on  upon  a  large  scale,  owing  to  the  incautious 
entrance  of  the  workmen  into  an  empty  fermenting  vat 
before  the  heavy  gas  has  had  time  to  escape.  The  plug  at 
the  bottom  should  be  left  open  after  the  liquor  has  run  off, 
to  assist  the  escape. 

Large  quantities  of  carbonic  anhydride  are  also  expelled 
in  the  process  of  burning  limestone  in  a  limekiln  ;  and  a 
similar  action  occurs  if  limestone  is  found  in  volcanic  dis- 
tricts, owing  to  the  action  upon  it  of  the  heat  beneath  the 
surface  of  the  earth,  in  consequence  of  which  immense 
volumes  of  the  gas  escape  from  craters  and  fissures  of  the 
soil.  The  springs  of  such  districts  are  often  highly  charged 
with  carbonic  acid,  and  the  gas  passes  off  with  effervescence 
when  the  water  comes  to  the  surface. 

Much  of  the  carbonic  acid  found  in  ordinary  spring  and 
river  water  is  furnished  by  the  gradual  oxidation,  in  the  pores 
of  the  soil,  of  the  vegetable  and  other  organic  matter  with 
which  they  had  been  before  contaminated. 

What  is  called  choke  damp  by  miners  is  also  principally 
composed  of  this  gas.  It  often  accumulates  in  old  pits  or 
wells,  and  in  the  abandoned  workings  of  mines.  No  one 
ought  ever  to  venture  into  such  places  without  first  trying 
whether  a  candle  will  burn  freely  in  the  pit  or  shaft,  although 
a  candle  will  burn  in  a  gas  which  is  dangerous  to  life. 

Whenever  charcoal,  or  any  substance  which  contains  car- 
bon, such  as  wood,  coal,  oil,  or  tallow,  is  burnt,  carbonic 
anhydride  is  formed  in  abundance. 

Exp.  64. — Kindle  a  piece  of  charcoal,  and  plunge  it  into  a 
bottle  of  oxygen  ;  it  will  burn  brilliantly.  After  the  combustion 
is  over,  shake  some  limewater  with  the  gas  which  remains ;  the 
immediate  precipitation  of  chalk  shows  that  carbonic  anhydride 
has  been  formed  abundantly. 

Exp.  65. — Hold  a  glass  jar  full  of  air  for  a  few  minutes  over 
a  piece  of  burning  charcoal ;  withdraw  the  jar,  and  close  the 


Ventilation. 


79 


Fig.  23. 


mouth  of  it  with  a  glass  plate.  Add  a  tablespoonful  of  lime- 
water,  and  shake  it  up  in  the  jar.  Chalk  will  immediately  be 
formed.  The  result  will  be  similar  if  the  jar  be  held  over  a  jet 
of  burning  coal  gas,  over  a  burning  candle,  or  over  the  flame  of 
a  spirit  lamp. 

Two  candles  of  6  to  the  pound,  in  burning,  may  be 
reckoned  to  produce  about  38  litres  of  carbonic  anhy- 
dride per  hour,  or  as  much  of  the  gas  as  would  be  generated 
by  the  respiration  of  a  man  of  ordinary  size  in  the  same 
time. 

Although  pure  carbonic  anhydride  is  heavier  than  air, 
both  the  products  from  a  burning  candle  and  air  which  has 
been  respired  are,  owing  to  the  heat  produced  in  eaph"ca^se> 
lighter  than  the  surrounding  air,  and  they  accumulate  in  the 
upper  part  of  an  inhabited  room. 
In  ventilating  such  a  room,  open- 
ings should  be  made  in  or  near 
the  ceiling  for  the  escape  of  the 
impure  heated  air,  while  the  free 
admission  of  fresh  air  should  be 
secured  near  the  floor. 

Exp.  66. — Fasten  a  piece  of  taper 
to  a  bit  of  cork,  and  place  it  in  a 
plate,  with  a  little  water.  Light  the 
taper;  then  cover  it  with  a  wide- 
necked  gas  jar,  and  over  the  neck 
of  the  jar  place  a  glass  gas-chimney, 
as  in  Fig.  23.  In  a  few  minutes  the 
taper  will  burn  dimly,  and  would 
soon  go  out ;  but  if  the  edge  of  the 
jar  be  slightly  raised  out  of  the 
water  in  the  plate,  air  will  enter  at 
the  bottom,  and  the  heated  impure 
air  will  pass  off  by  the  chimney.  The  course  of  the  current  may 
be  watched  by  means  of  the  smoke  from  a  smouldering  bit  of 
brown  paper,  which  will  follow  the  movements  of  the  air,  if 
brought  near  enough.  Instead  of  lifting  the  edge  of  the  jar, 


8o  Decomposition  of  Carbonic  Anhydride. 

divide  the  air-way  through  the  chimney  by  placing  a  long  slip 
of  card  down  the  middle;  a  downward  current  will  then  be 
established  on  one  side  of  the  card,  and  an  ascending  current 
on  the  other,  and  the  taper  will  burn  freely. 

It  is  on  this  principle  that  small  mines  are  often  ventilated 
for  a  time,  the  shaft  being  divided  by  a  wooden  partition 
into  a  downcast  and  an  upcast  shaft.  In  the  best  ventilated 
mines,  however,  this  is  done  by  two  separate  shafts,  sunk  at 
some  distance  from  each  other,  and  in  one  of  these  shafts  a 
fire  is  kept  burning,  for  the  purpose  of  producing  an  ascend- 
ing current  of  hot  air.  Ventilation  by  means  of  fans  driven 
by  machinery  is,  however,  both  much  safer  and  more  effectual 
in  producing  the  necessary  movement  of  the  air. 

Carbon  may  without  difficulty  be  separated  from  carbonic 
anhydride. 

Exp.  67. — Cause  a  current  of  the  gas  to  pass  through  a 
drying-tube  containing  calcic  chloride  (Fig.  24),  and  then  through 


Fig.  24. 


a  bulb  tube  containing  a  small  piece  of  potassium.  Heat  the 
potassium  in  the  gas  :  it  will  soon  take  fire,  and  burn  brilliantly. 
Let  the  tube  cool,  and  then  plunge  it  into  water. 

In  this  experiment  potash  is  formed  in  the  tube  at  the 
expense  of  oxygen  derived  from  the  gas  ;  the  alkali  is  dis- 
solved by  the  water,  and  black  particles  of  charcoal  become 
diffused  through  the  liquid. 

Exp.  68. — Kindle  a  strip  of  magnesium  foil,  by  holding  it 


Synthesis  of  Carbonic  Anhydride.  8 1 

with  the  tongs  in  the  flame  of  a  spirit  lamp ;  and  when  burning 
brightly,  introduce  it  into  a  jar  filled  with  carbonic  anhydride. 
The  metal  will  continue  to  burn  ;  white  flakes  of  magnesia, 
mixed  with  black  particles  of  carbon,  will  be  deposited.  Add  a 
little  dilute  nitric  acid  :  this  will  dissolve  the  magnesia,  and 
leave  the  carbon. 

Carbonic  anhydride  is  not  only  absorbed  by  limewater, 
but  it  is  also  quickly  absorbed  by  any  alkali,  such  as  a  solu- 
tion of  potash. 

Exp.  69. — Fill  a  strong  graduated  test-tube  with  carbonic  an- 
hydride by  displacement,  and  invert  it  in  a  deep  glass  containing 
mercury,  as  shown  in  Fig  8.  Then  introduce  the  curved  beak 
of  a  pipette,  filled  with  a  strong  solution  of  potash,  beneath  the 
edge  of  the  tube,  and  blow  from  the  lungs  with  just  sufficient 
force  to  drive  a  few  drops  of  the  liquid  into  the  tube.  The  solu- 
tion of  potash  will  quickly  absorb  the  gas,  and  mercury  will 
rise  in  the  tube. 

A  strong  solution  of  potash  is  in  continual  use  in  the 
laboratory  for  separating  carbonic  anhydride  from  other 
gases  which,  like  oxygen,  nitrogen,  and  hydrogen,  are  in- 
soluble in  the  potash  solution.  In  this  way  it  is  easy  to 
estimate  the  quantity  of  carbonic  anhydride  in  respired  air. 

We  have  thus  proved  by  synthetic  experiments  that  when 
charcoal  is  burned  in  air  or  in  oxygen,  carbonic  anhydride  is 
formed ;  and  we  have  found  by  analysis  that  the  gas  con- 
tains both  oxygen  and  charcoal.  It  may  be  shown  that  it 
contains  nothing  but  carbon  and  oxygen,  and  the  exact  pro- 
portions may  be  determined  by  means  of  the  apparatus 
shown  in  Fig.  25. 

A  is  a  gas-holder  filled  with  pure  oxygen,  B  a  strong  solu- 
tion of  potash,  D  a  tube  filled  with  calcic  chloride  in  lumps, 
E  a  sheet-iron  furnace  containing  a  tube  of  hard  glass  :  at  F, 
within  the  tube,  is  a  platinum  tray  containing  the  carbon  ;  G  is 
a  tube  containing  calcic  chloride,  H  a  series  of  bulbs  filled 
with  solution  of  potash,  while  i  is  a  tube  filled  with  lumps  of 
potash. 

The  platinum  tray  with  the  carbon,  whether  in  the  form  of 
G 


82  Synthesis  of  Carbonic  Anhydride. 

diamond,  graphite,  or  charcoal,  is  weighed  accurately  at 
first.  Then  the  oxygen  dried  in  its  passage  is  allowed  to 
stream  slowly  through  the  tube,  which  is  gradually  made  red 
hot  by  placing  glowing  charcoal  round  it  in  the  furnace. 
The  carbon  in  the  platinum  tray  burns  brilliantly  in  the 
stream  of  oxygen,  and  becomes  converted  into  carbonic  anhy- 
dride. The  tube  should  also  contain  cupric  oxide,  by  which 
any  trace  of  carbonic  oxide  which  might  be  formed  would  be 
at  once  converted  into  the  anhydride.  This  is  completely 
arrested  by  the  potash  in  the  bulb  tubes  H,  no  gas  but  pure 


Fig.  25. 


and  dry  oxygen  escaping  into  the  air.  The  gain  in  weight 
of  H  and  i  together  shows  how  much  carbonic  anhydride  has 
been  formed.  The  loss  of  weight  of  the  platinum  tray  F 
shows  how  much  carbon  has  been  burnt,  and  the  difference 
between  this  weight  and  that  of  the  carbonic  anhydride 
shows  how  much  oxygen  has  combined  with  the  carbon. 
No  chemical  experiment  has  ever  been  made  with  greater 
care  than  this  for  the  purpose  of  arriving  at  accurate  results, 
since  the  composition  of  carbonic  anhydride  is  a  fundamental 
datum  in  all  analyses  of  organic  compounds.  It  has  been 
found  by  repeated  trials  of  this  process  that  1 2  grams  of  car- 
bon require  exactly  32  grams  of  oxygen  to  convert  them  into 
44  grams  of  carbonic  anhydride ;  so  that,  assuming  for  the 
present  the  atomic  weight  of  carbon  to  be  12,  the  molecular 
weight  of  a  carbonic  anhydride  is  44,  and  the  formula  re- 
presenting its  composition  is  CO2. 


Carbonic  Acid  in  the  Atmosphere.  83 

If  carbon  be  burned  in  a  jar  of  oxygen  over  mercury,  so 
as  to  prevent  any  loss  of  the  gas,  it  is  found  that  the  gas, 
when  it  has  cooled  down  again  and  is  measured  with  due 
care,  is  not  altered  in  bulk.  The  carbonic  anhydride  formed 
occupies  the  same  volume  as  the  oxygen  which  has  entered 
into  its  composition,  so  that  the  gas  contains  its  own  bulk 
of  oxygen. 

Carbonic  acid,  though  a  weak  one,  forms  a  numerous  and 
important  series  of  salts,  called  carbonates.  Except  those  of 
the  alkaline  metals,  they  are  nearly  insoluble  in  water ;  and 
all,  whether  soluble  in  water  or  not,  dissolve  with  effer- 
vescence in  dilute  nitric  acid.  The  gas  which  comes  off 
is  colourless,  with  scarcely  any  smell;  and  if  passed  into 
limewater,  it  makes  it  turbid,  thus  showing  it  to  be  carbonic 
acid. 

Many  of  the  carbonates  occur  in  immense  quantities  as 
natural  products,  particularly  calcic  and  magnesic  car- 
bonates. 

The  quantity  of  carbonic  anhydride  in  the  atmosphere  is 
tending  continually  to  increase,  in  consequence  of  the 
numerous  chemical  processes  by  which  it  is  being  produced; 
and  it  would  accumulate  to  a  serious  extent,  were  it  not  pre- 
vented by  a  remarkable  counteracting  power  possessed  by 
growing  plants.  The  green  parts  of  plants,  when  in  the 
sun's  light,  decompose  carbonic  acid,  and  lay  up  the  carbon 
in  the  wood  and  other  parts,  whilst  they  give  back  most  of 
the  oxygen  to  the  air,  thus  converting  again  into  fuel  that 
material  which  has  been  diffused  through  the  atmosphere, 
and  has,  by  being  burned,  lost  for  the  time  its  chemical 
activity.  The  rain  as  it  falls  dissolves  the  carbonic  anhy- 
dride, and  carries  it  down  to  the  earth;  and  the  roots  of  the 
plants  absorb  it,  and  carry  it  up  into  the  leaves,  where  it 
undergoes  the  necessary  chemical  change,  so  long  as  the  sun's 
rays  fall  upon  the  plant.  In  the  dark,  no  such  removal  of 
carbon  from  the  gas  and  restoration  of  oxygen  to  the  air 
occurs. 


84 


Varieties  of  Carbon. 


Fig.  26. 


Exp.  70.— Into  a  small  gas  jar  (Fig.  26)  fit  a  good  cork,  instead 
of  the  stopper,  and  pass  a  test-tube  tightly  through  a  hole  bored 
through  the  cork.  Place  the  jar  in  a  large  beaker  filled  with 
spring  water,  which  has  been  mixed  with 
a  fourth  of  its  bulk  of  solution  of  carbonic 
acid  in  water.  Fill  the  tube  with  water, 
and  place  it  in  the  neck  of  the  jar,  having 
introduced  a  few  sprigs  of  mint  or  the  leafy 
branches  of  any  succulent  plant  in  the 
jar,  and  then  expose  it  for  an  hour  or  two 
in  direct  sunshine.  Bubbles  of  gas  will  be 
seen  studding  the  leaves ;  and  on  shaking 
the  jar,  these  will  become  detached,  and 
will  rise  into  the  test-tube.  After  a  time 
the  cork  and  tube  may  be  withdrawn, 
keeping  the  mouth  of  the  tube  beneath 
the  surface  of  the  water ;  then  close  it  with 
the  thumb,  turn  the  tube  mouth  upwards, 
and  test  the  gas  with  a  glowing  splinter.  The  wood  will  burst 
into  a  blaze,  showing  that  the  gas  consists  mainly  of  oxygen. 

(18)  CARBON:  Smyb.  C;  Atomic  Wt.  12;  Sp.  Gr.  as 
diamond,  about  3-4. 

Carbon  is  an  elementary  body  of  the  greatest  importance, 
and  it  occurs  in  various  familiar  forms,  viz.  naturally  as 
diamond,  and  as  graphite  or  black-lead,  as  well  as  less  pure 
in  the  different  artificial  substances  known  as  charcoal  and 
coke.  It  is  also  abundant  in  combination  :  chalk  contains 
not  less  than  an  eighth  of  its  entire  weight  of  carbon,  and 
magnesic  carbonate  more  than  one-seventh.  Carbon  also 
occurs  combined  with  other  elements ;  for  it  is  the  cha- 
racteristic constituent  of  those  substances  which  are  called 
organic  and  are  of  vegetable  or  animal  origin. 

a.  The  diamond  is  the  hardest  of  known  substances,  and 
the  most  valuable  of  gems.  It  consists  of  pure  carbon 
crystallised  in  forms  derived  from  the  regular  octahedron  and 
dodecahedron,  and  often  in  the  form  of  rolled  pebbles,  with 
a  dingy  exterior,  which  would  cause  them  often  to  be  over- 


Diamond — Plum  bago.  8  5 

looked  by  an  unskilled  observer.  The  diamond  can  only  be 
cut  and  polished  by  grinding  it  with  its  own  powder.  Its 
most  important  use  is  familiar  to  us  in  the  hands  of  the 
glazier  for  cutting  sheets  of  glass.  Owing  to  its  rarity,  its 
high  refracting  power,  and  brilliant  lustre,  it  has  been  prized 
for  ornamental  purposes  from  time  immemorial. 

Diamond  may  be  burned  in  oxygen  gas,  when  it  con- 
sumes away  almost  without  residue.  Twelve  mgrams.  of 
diamond  have  been  found  to  yield  when  thus  burned  exactly 
44  mgrams.  of  carbonic  anhydride,  and  no  other  product.  It 
has  never  been  melted.  It  is  a  non-conductor  of  electricity, 
though  other  forms  of  carbon  conduct  it  well.  When  heated 
intensely  in  the  arc  of  the  voltaic  battery,  as  soon  as  it 
becomes  white  hot,  it  swells  up,  loses  its  transparency, 
acquires  the  power  of  conducting  electricity,  and  is  con- 
verted into  a  black  opaque  mass  resembling  coke. 

b.  Plumbago,  or  gmphite,  frequently  from  its  appearance 
called  black-lead,  though  it  contains  no  lead,  is  another  form 
in  which  carbon  is  found  naturally,  but  in  tolerable  quantity. 
It  has  a  sp.  gr.  of  about  2-2,  and  occurs  sometimes  in  crys- 
talline six-sided  plates.  It  has  a  leaden-grey  lustre,  leaves  a 
streak  upon  paper  on  which  it  is  rubbed,  on  which  account 
the  finest  kind  is  used  in  making  artists'  drawing  pencils.  It 
is  a  good  conductor  of  electricity.  When  it  is  burned  in 
oxygen,  it  always  leaves  from  2  to  5  per  cent,  of  ash,  which, 
however,  is  not  a  necessary  part  of  it.  The  gas  which  it 
furnishes  when  thus  burned  in  oxygen  is  pure  carbonic 
anhydride.  Owing  to  its  perfect  indifference  to  the  action 
of  oxygen  at  common  temperatures,  it  forms  a  serviceable 
coating  for  the  protection  of  ironwork  from  rust,  as  is  com- 
monly practised  with  fire-grates  and  stoves.  Graphite,  when 
mixed  with  clay,  is  often  made  into  crucibles,  because  they 
are  not  liable  to  crack  in  the  fire.  Molten  iron  dissolves 
carbon  readily  ;  much  of  it  separates  from  the  iron  again  if 
the  melted  metal  is  allowed  to  cool  slowly.  It  is  then  in  the 
form  of  graphite. 


86  Pit  Coal — Anthracite. 

Pit  Coal. — This  is  one  of  the  most  important  natural  sub- 
stances rich  in  carbon.  It  is  a  material,  of  vegetable  origin, 
which  has  become  altered  during  the  lapse  of  ages,  while 
exposed,  under  great  pressure  in  the  strata  of  the  earth,  to 
the  combined  action  of  water  holding  in  solution  oxygen 
derived  from  the  air,  and  moderate  heat.  The  composition  of 
pit  coal  varies  greatly  according  to  the  length  of  time  during 
which  it  has  been  thus  acted  on,  the  older  deposits  being 
those  which  contain  the  largest  proportion  of  carbon.  The 
elements  of  which  the  original  vegetation  consisted  are  car- 
bon in  large  proportion,  oxygen  in  smaller  quantity,  still  less 
hydrogen,  and  a  very  small  proportion  of  nitrogen^  but 
besides  these  there  is  a  variable  quantity  of  saline  and  earthy 
substances  which  always  occur  in  vegetable  juices ;  added 
to  which  are  earthy  impurities  derived  from  the  adjacent 
strata,  as  well  as  a  portion  of  iron  pyrites  (FeS2),  which  is 
always  gradually  formed  in  the  coal.  When  coal  is  burned 
in  the  open  fire,  if  there  be  a  sufficient  supply  of  air,  the 
carbon  becomes  carbonic  anhydride,  the  hydrogen  burns 
into  water,  the  nitrogen  escapes  chiefly  as  gas,  and  the  ash 
which  remains  is  composed  of  the  saline  and  earthy  residue. 

Much  of  the  South  Wales  coal  is  of  the  modification  called 
culm  or  anthracite,  which  contains  upwards  of  90  per  cent, 
of  carbon,  and  but  little  volatile  matter.  It  burns  without 
flame,  and  with  a  steady  glow.  House  coal,  such  as  is  used 
in  London,  is  of  a  different  kind.  It  softens  when  heated, 
and  forms  a  pitchy  or  bituminous  mass,  which  causes  the 
pieces  to  cake  together.  Such  coal  is  never  burned  com- 
pletely, even  in  an  open  fire ;  but  in  the  act  of  burning  it 
gives  off  a  quantity  of  gaseous  or  tarry  matter,  holding  finely 
divided  carbon  or  soot  in  suspension.  When  a  quantity  of 
fresh  coal  of  this  kind  is  thrown  upon  a  hot  fire,  it  at  once 
begins  to  be  decomposed ;  considerable  quantities  of  the 
compounds  of  carbon  and  hydrogen  are  formed,  and  pass 
off  in  the  condition  of  gas  or  vapour.  A  portion  of  these  sub- 
stances immediately  takes  fire,  and  burns  with  a  bright  light 


Combustion  and  Distillation  of  Coal.  87 

and  a  smoky  flame ;  but  a  large  portion  of  them,  when  they 
pass  over  the  glowing  embers,  is  more  or  less  completely 
decomposed;  the  carbon  and  hydrogen  become  partially 
separated  from  each  other  in  a  part  of  the  fire  where  there  is 
but  little  uncombined  oxygen  ;  the  hydrogen,  being  the  more 
combustible  element  of  the  two,  seizes  upon  such  oxygen  as 
it  finds,  or  else  it  escapes  unburnt  in  the  form  of  gas  ;  while 
the  carbon,  still  containing  a  notable  proportion  of  hydro- 
gen, is  carried  away  in  very  fine  particles,  and  passes  off  as 
smoke,  suspended  in  the  heated  gases. 

The  formation  of  this  black  smoke  may,  however,  be  pre- 
vented by  throwing  the  coal  upon  the  fire  in  small  quantities 
at  a  time,  taking  care  to  keep  up  a  strong  steady  heat,  so  as 
to  consume  the  gases  as  they  are  formed ;  but  this  can  only 
be  secured  by  a  sufficient  supply  of  atmospheric  air,  a  con- 
dition not  so  easily  fulfilled  in  manufacturing  furnaces  as 
might  be  expected,  though  with  proper  care  it  can  be  done. 

When  bituminous  coal  is  heated  in  long  closed  iron 
cylinders,  out  of  contact  with  air,  a  large  quantity  of  gas 
and  of  tar  is  formed ;  they  contain  the  oxygen,  hydrogen, 
nitrogen,  and  part  of  the  carbon  of  the  coal,  while  the 
greater  portion  of  the  carbon  is  left  behind  as  a  porous  mass, 
called  coke.  Coke  resembles  graphite  in  properties,  but  it 
retains  all  the  ash  and  earthy  impurities  of  the  coal.  It 
burns  with  a  steady  glow,  without  emitting  flame  or  smoke ; 
it  is  less  combustible  than  coal,  and  requires  a  brisk  current 
of  air  to  keep  it  burning.  The  more  highly  the  coke  is  heated 
during  its  preparation,  the  more  compact  does  it  become, 
the  better  does  it  conduct  heat,  and  the  more  slowly  does  it 
burn. 

Exp.  71. — Get  a  blacksmith  to  weld  up  one  end  of  a  wrought- 
iron  gas-pipe  25  mm.  (i  inch)  in  diameter,  and  50  centim.  long. 
Fit  a  cork  and  a  bent  tube  to  the  open  end ;  put  from  50  to  100 
grams  of  coarsely  broken  coal  into  the  iron  tube ;  *  heat  the 

*  A  hard  glass  tube  may  be  used  instead  of  the  iron  tube,  and  may 
be  heated  in  a  flame,  but  it  does  not  yield  the  gas  so  easily. 


88  Coke — Preparation  of  Charcoal. 

closed  end  in  a  common  fire,  and  direct  the  gas  into  the  pneu- 
matic trough.  Some  tarry  matter  will  pass  over,  and  a  con- 
siderable quantity  of  gas  may  be  collected,  which  will  burn  with 
a  bright  flame.  When  all  the  gas  appears  to  have  been  driven 
off.  take  the  tube  out  of  the  fire,  let  it  cool,  and  then,  with  an 
iron  rod,  detach  what  is  left  in  the  inside  of  the  tube.  It  will  be 
found  to  be  common  coke.  Put  some  of  this  coke  in  a  small 
open  clay  crucible,  and  heat  it  in  the  fire  :  the  coke  will  gra- 
dually burn  away,  leaving  nothing  but  a  little  ash. 

The  dense  coke  required  for  burning  in  the  powerful  draught 
created  under  the  boiler  of  a  locomotive  engine  is  usually 
prepared  by  burning  the  coke  in  massive  brick  ovens,  in 
each  of  which  several  tons  of  coal  can  be  charred  in  a  single 
operation,  the  ovens  being  provided  with  a  sliding  door,  for 
regulating  the  admission  of  air,  which  plays  over  the  surface  of 
the  heap  and  burns  off  the  volatile  matters,  and  so  chars  the 
whole  mass  at  a  very  high  temperature,  each  charge  requir- 
ing 48  hours  for  its  conversion  into  coke. 

If,  instead  of  heating  coal  in  an  iron  retort,  wood  be 
treated  in  the  same  way,  a  still  larger  quantity  of  volatile 
and  liquid  products  will  be  given  off,  and  what  is  left  behind 
is  a  black  porous  substance,  of  the  same  shape  as  the  wood, 
familiarly  called  charcoal.  Wood  tar,  vinegar,  and  wood 
naphtha  are  among  the  liquid  products,  which  redden  litmus 
paper  strongly,  but  the  gas  has  little  illuminating  power, 
more  compact  charcoal,  better  suited  for  use  as  fuel,  is  made 
by  burning  wood  in  heaps.  A  stake  is  driven  into  the 
ground,  brushwood  is  placed  round  the  bottom,  and  logs  of 
wood  are  piled  up  regularly  around  the  stake.  The  heap  thus 
formed  is  often  10  metres  or  more  in  diameter;  it  is  covered 
with  powdered  charcoal,  turf,  and  earth.  It  is  then  kindled 
by  introducing  lighted  fagots  at  openings  left  for  the  pur- 
pose. Large  quantities  of  moisture  are  driven  off,  and  the 
fire  spreads  gradually  through  the  mass,  the  admission  of  air 
being  carefully  regulated,  so  to  cause  one  part  of  the  wood  in 
burning  completely  to  char  and  drive  off  the  volatile  matter: 


Charcoal—  Carbon  Fuel  89 

from  the  rest.  When  gas  and  vapours  cease  to  come  off,  the 
fire  is  extinguished  by  closing  all  the  openings  for  the 
admission  of  air,  and  adding  a  thicker  layer  of  mould  and 
turf.  Such  a  heap  takes  nearly  a  month  to  burn  out,  and 
never  furnishes  more  charcoal  than  a  quarter  of  the  weight 
of  the  wood  used. 

The  gas  and  the  liquids  which  are  obtained  from  the  coal 
and  the  wood  during  this  process  of  destructive  distilla- 
tion do  not  exist  ready  formed  in  these  substances.  They 
are  the  result  of  chemical  changes  produced  under  the 
influence  of  the  heat ;  the  carbon  and  hydrogen  combine 
together  in  new  proportions,  and  thus  furnish  substances 
quite  different  in  properties  from  the  original  coal  and 
wood. 

Nearly  all  vegetable  and  animal  matters,  when  heated  out 
of  contact  with  air,  furnish  charcoal  more  or  less  pure. 

Exp.  72. — Put  a  few  pieces  of  wood  into  a  clay  crucible  ; 
cover  the  wood  completely  with  sand,  and  heat  the  whole  for 
20  minutes  in  a  fire.  Gas  will  be  given  off,  and  burn.  Take 
the  crucible  out  of  the  fire,  let  the  whole  cool,  then  empty  the 
crucible  :  the  wood  will  be  found  to  be  converted  into  charcoal. 

Charcoal  gives  out  more  heat  in  burning  than  an  equal 
bulk  of  wood,  as  the  moisture  and  volatile  matters  given  off 
by  the  wood  carry  away  much  of  the  heat  in  the  latent  state. 
But  in  the  economy  of  fuel  it  is  not  sufficient  to  consider 
simply  the  absolute  amount  of  heat  which  a  given  weight  of 
it  emits  in  burning.  A  fuel  which  burns  with  flame  is 
necessary  where  it  is  desired  to  communicate  an  elevated 
and  uniform  temperature  to  objects  at  a  distance  from  the 
fire-grate,  as  in  heating  glass  pots  or  the  contents  of  a  porce- 
lain kiln  ;  whilst  in  heating  boilers  and  objects  where  direct 
radiation  from  the  fuel  can  act  fully,  coke,  charcoal,  or 
anthracite  is  very  valuable;  and  in  an  ordinary  open  fire  these 
same  fuels  radiate  much  more  heat  into  the  room,  though 
they  do  not  look  so  cheerful,  as  the  bituminous  coal,  with  its 
fitful,  flickering  flame. 


yb  Lamp-black — Bone  Charcoal. 

There  are  other  forms  of  carbon  besides  coke  and  char- 
coal which  are  manufactured  for  use  in  the  arts.  One  of 
these  is  lamp-black,  the  basis  of  printers'  ink,  and  the  most 
permanent  of  black  pigments.  It  is  obtained  by  heating  in 
an  iron  pot  vegetable  matters,  such  as  rosin  and  pitch,  which 
are  rich  in  hydrogen  and  carbon.  The  vapours  are  burned 
in  a  current  of  air  insufficient  for  complete  combustion ;  the 
hydrogen,  which  is  the  more  inflammable  element,  burns 
first,  leaving  the  carbon  in  a  finely  divided  state. 

Exp.  73. — Set  fire  to  a  little  rosin  in  a  small  iron  spoon; 
hold  a  cold  white  plate  in  the  flame.  Abundance  of  soot  will 
be  deposited  upon  it.  The  flame  of  a  candle  or  of  an  oil  lamp 
will  give  a  similar  result. 

Animal  charcoal,  or  ivory  black,  is  prepared  by  heating 
bones  in  iron  retorts.  It  is  used  largely  by  the  sugar  refiners 
for  removing  colour  from  syrups. 

Exp.  74. — Place  a  few  pieces  of  mutton  shank  or  other  bone 
in  a  clay  crucible ;  cover  them  completely  with  sand,  and  heat 
the  crucible  for  half  an  hour  in  a  common  fire.  Take  it  out,  and 
when  cold  crush  the  burnt  bones  to  a  coarse  powder.  Dissolve 
25  grams  of  coarse  brown  sugar  into  5  or  6  times  its  weight  of 
water ;  divide  the  solution  into  two  parts,  and  pour  one  half 
upon  about  20  grams  of  the  crushed  bone  charcoal,  and  let  it 
stand  for  an  hour;  then  filter  the  solution  through  blotting- 
paper.  In  order  to  prepare  this  filter,  fold  a  square  of  paper,  as 


Fig.  27. 


shown  in  Fig.  27,  first  into  half,  and  then  again  into  a  quarter  of 
its  first  size ;  cut  off  the  edges  in  the  direction  of  the  dotted 
line  shown  in  the  left-hand  figure,  open  out  the  folded  paper, 
and  drop  it  into  a  funnel  a  little  larger  than  the  paper  cone. 


Antiseptic  powers  of  Charcoal.  gi 

The  liquor  which  runs  through  will  be  found,  when  compared 
with  the  original  syrup,  to  have  lost  most  of  its  brown  colour, 
which  is  caused  by  a  substance  that  remains  adherent  to  the 
charcoal.  Wash  out  the  syrup  ;  then  pour  a  little  solution  of 
potash  upon  the  charcoal  in  the  filter.  The  brown  colouring 
matter  will  become  again  dissolved  by  the  alkaline  solution  as  it 
runs  through. 

Port  wine,  porter,  and  many  other  coloured  liquids  may 
be  deprived  of  their  colour  in  a  similar  manner. 

Wood  charcoal  produces  decolourising  effects  similar  to 
those  obtained  with  animal  charcoal,  though  it  is  less  power- 
ful. Charcoal,  like  most  porous  bodies,  condenses  many 
gases  and  vapours  in  its  pores. 

Exp.  75. — Weigh  a  piece  of  freshly  burned  charcoal  as  soon 
as  it  is  cold;  leave  it  exposed  to  the  air  for  24  hours,  and  weigh 
it  again  :  it  will  be  found  to  be  heavier.  Place  the  charcoal  in  a 
glass  tube,  and  heat  it  over  a  lamp  :  a  good  deal  of  moisture 
will  be  driven  off,  and  will  become  condensed  on  the  cold  sides 
of  the  tube.  This  moisture  was  absorbed  from  the  air  by  the 
charcoal. 

Exp.  76. — Place  a  piece  of  raw  meat  in  a  glass  jar,  and  cover 
it  with  a  layer  of  charcoal  powder  25  mm.  thick,  and  leave  it  for 
several  days.  No  offensive  odour  will  be  perceived,  even  in  the 
height  of  summer. 

The  meat  may  even  become  putrid,  but  the  noxious  and 
offensive  gases  which  would  otherwise  escape  are  absorbed 
by  the  charcoal,  and  are  slowly  oxidized  within  in  its  pores 
by  the  action  of  the  oxygen,  condensed  by  the  charcoal  from 
the  surrounding  air.  Shallow  trays  of  wood  charcoal  are  of 
use  in  sick  rooms,  owing  to  their  exerting  this  absorbent  and 
purifying  action  upon  the  atmosphere.  They  preserve  their 
power  for  an  unlimited  time,  the  carbon  of  the  absorbed 
organic  matter  being  dissipated  as  carbonic  anhydride,  and 
the  hydrogen  as  water. 

Owing  to  this  absorbent  action,  charcoal  forms  a  valuable 
material  in  the  construction  of  filters  for  water,  as  it  acts 
powerfully  on  many  of  the  organic  impurities. 


92  A  Hot  ropy. 

Exp.  77. — Shake  up  some  stagnant  water  which  has  been 
kept  till  it  smells  offensively  with  a  little  powdered  charcoal. 
In  an  hour  it  will  have  lost  all  its  disagreeable  odour. 

Carbon  is  indestructible  by  exposure,  at  ordinary  tem- 
peratures, to  the  air  or  to  water.  Hence  it  is  a  common 
practice  to  char  the  surface  of  wooden  piles  before  driving 
them,  and  to  prepare  the  interior  of  casks  and  water-butts  in 
a  similar  manner. 

Charcoal  and  the  common  varieties  of  carbon,  however, 
combine  rapidly  with  oxygen  at  high  temperatures ;  and  their 
attraction  for  oxygen  is  so  great  that  carbon  in  some  form 
or  other  is  employed  to  remove  oxygen  from  its  combinations 
with  other  elements,  particularly  from  the  oxides  of  the 
metals,  which,  when  heated  with  carbon,  are  reduced  or  brought 
back  to  the  metallic  state.  Hence  carbon  is  spoken  of  as 
a  reducing  agent  by  the  metallurgist.  This  action  may  be 
shown  as  follows : — 

Exp.  78. — Mix  in  a  mortar  20  grams  of  litharge  or  lead  oxide 
(PbO)  with  40  grams  of  common  salt  and  I  gram  of  powdered 
charcoal ;  cover  it  with  a  little  more  salt,  and  place  the  mixture 
in  a  small  clay  crucible ;  heat  it  to  bright  redness  in  the  fire. 
When  the  mixture  is  melted,  take  the  crucible  out  of  the  fire  and 
let  it  cool.  When  quite  cold,  break  the  crucible,  and  a  bead  of  lead 
will  be  found  at  the  bottom,  under  the  melted  salt,  the  carbon 
having  taken  the  oxygen  from  the  oxide  of  lead. 

Twelve  grams  of  pure  charcoal,*  free  from  ash,  when 
burned  in  a  current  of  oxygen,  yield  exactly  44  grams  of 
carbonic  anhydride.  Equal  weights  of  diamond,  plumbago, 
and  charcoal  are  thus  shown,  when  heated  with  oxygen,  to 
yield  equal  weights  of  carbonic  anhydride;  and  though  so 
different  in  appearance,  they  still  consist  of  the  same  ele- 
mentary body.  Many  of  the  elements  have  the  power  of 
assuming  forms  which  differ  in  appearance  and  properties 
quite  as  much  as  these  three  different  conditions  of  carbon. 
Such  elements  are  then  said  to  assume  different  allotropic 

*  Common  charcoal,  however,  always  retains  a  little  hydrogen. 


Carbonic  Oxide.  93 

states,  which  is  as  much  as  to  say  that  in  each  different 
modification,  though  all  the  atoms  are  alike,  yet  they  are 
arranged  in  a  different  way.  The  atoms  of  carbon,  for  in- 
stance, which  constitute  diamond,  are  arranged  very  dif- 
ferently from  those  which  form  graphite,  and  the  atoms  of 
carbon  in  charcoal  are  differently  arranged  from  those  of 
either  diamond  or  graphite. 

Carbon  unites  with  sulphur  if  strongly  heated  with  it,  and 
if  heated  intensely  in  hydrogen  gas  a  small  quantity  of 
acetylene  (C2H2)  is  formed ;  but  it  has  little  tendency  to 
unite  with  the  other  non-metals.  Some  of  the  compounds 
of  carbon  with  the  metals  are  important.  They  are  termed 
Carbides. 

(19)  CARBONIC  OXIDE:  Symb.  CO;  Atomic  and Mol.  Wt. 
28;  Sf.  Gr.  0-967;  Rd.  Wt.  14. 

Carbon  forms  only  two  compounds  with  oxygen,  so  far  as 

known.  One  of  these  is  carbonic  anhydride;  the  other, 
,lso  a  gas,  containing  just  half  as  much  oxygen,  is  called  car- 
bonic oxide. 

Exp.  79. — Fill  the  iron  tube  (Fig.  13)  with  small  lumps  of 
charcoal,  instead  of  with  iron  turnings;  make  it  red  hot  in  the 
urnace,  and  drive  steam  over  the  ignited  charcoal.  Collect  the 
gas  which  is  formed  :  it  will  burn  with  a  pale  blue  flame.  Shake 
up  a  little  limewater  with  another  of  the  jars  of  gas  :  it  will  be 
rendered  milky. 

Three  gases,  viz.  hydrogen,  carbonic  anhydride,  and  car- 
bonic oxide,  are  formed  in  this  case.  These  changes  may 
be  thus  explained  :  the  carbon  takes  the  oxygen  from  the 
vater,  forming  a  mixture  of  carbonic  oxide  and  carbonic 
nhydride,  whilst  its  hydrogen  is  set  at  liberty — 

H2O  +  C  =  CO  +  H2;  and  2H2O  +  C  =  CO2  +  2H2. 

Exp.  80. — Mix  some  chalk  with  its  own  weight  of  iron  filings  ; 
place  40  or  50  grams  of  the  mixture  in  an  iron  tube  arranged 
i  in  Exp.  71.     Heat  the  closed  end  of  the  iron  tube  to  redness 
L  the  fire  :  a  gas  comes  off,  which  may  be  collected  oVer  water. 


94  Experiments  with  Carbonic  Oxide. 

The  heat  expels  carbonic  anhydride  from  the  chalk,  and 
the  iron  takes  half  the  oxygen  from  the  carbonic  anhydride, 
and  forms  carbonic  oxide  ;  CaO,  CO2  +  Fe  becoming 
CaO  +  FeO  +  CO. 

Exp.  8 1. — Plunge  a  taper  into  a  jar  of  the  gas  ;  the  light  will 
be  extinguished,  but  the  gas  will  burn  at  the  mouth  of  the  jar 
with  a  blue  flame. 

Carbonic  oxide  is  often  formed  largely  in  stoves  and 
furnaces,  owing  to  the  manner  in  which  heated  carbon  acts 
on  carbonic  anhydride.  When  air  enters  at  the  bottom  of 
a  clear  fire,  the  oxygen  burns  a  part  of  the  carbon  at  once 
into  carbonic  anhydride;  and  this  gas,  with  the  nitrogen  of 
the  air,  passes  through  the  red-hot  embers.  The  nitrogen 
undergoes  no  change,  but  the  carbonic  anhydride  takes  up  a 
further  quantity  of  carbon,  and  becomes  converted  into 
carbonic  oxide  :  C  +  CO2  =  2  CO,  the  carbonic  anhydride 
being  exactly  doubled  in  bulk  in  consequence.  This  mode 
of  the  formation  of  the  gas  is  important,  because,  if  the 
supply  of  air  to  a  furnace  is  too  small,  the  carbonic  oxide 
passes  up  the  chimney  unburnt,  and  much  heat  is  wasted, 
which  would  be  saved  if  the  gas  were  properly  consumed. 
Sometimes  we  see  the  carbonic  oxide  burning  on  the 
top  of  a  clear  glowing  fire,  where  it  again  mixes  with 
fresh  oxygen  of  the  air  while  the  gas  is  still  hot  enough  to 
burn.  Furnaces  are  sometimes  made  to  supply  air  just 
above  the  top  of  the  fire-grate,  so  as  to  burn  the  carbon 
oxide  completely. 

Exp.  82. — Make  the  iron  tube  and  charcoal  red  hot,  as  in 
Exp.  79;  but  instead  of  sending  steam  through  it,  attach  to  the 
tube  a  bottle  which  is  giving  off  carbonic  anhydride  steadily. 
Collect  the  gas  over  water  as  it  escapes  at  the  other  end  :  it  will 
burn  with  the  blue  flame  which  distinguishes  carbonic  oxide. 

Exp.  83. — Collect  some  carbonic  oxide  in  a  jar  provided  with 
a  stop-cock  at  the  top,  or  fitted  up  in  the  way  directed  in  Exp.  48 
(Fig.  1 6),  with  a  flexible  tube  and  screw-tap.  Fasten  a  glass  quill 
tube  to  the  vulcanised  tube ;  depress  the  jar  in  the  pneumatic 
trough,  and  allow  a  little  of  the  gas  to  escape,  by  relaxing  the 


Preparation  of  Carbonic  Oxide.  95 

screw ;  set  fire  to  the  issuing  gas,  and  hold  over  it  a  small  gas 
jar.  No  water  will  be  condensed  on  its  sides  ;  but  if  the  jar  be 
closed  with  a  glass  plate,  and  limewater  be  poured  into  it,  a 
white  precipitate  of  chalk  will  be  produced. 

The  carbonic  oxide  in  burning  becomes  converted  into 
carbonic  anhydride ;  2  litres  of  carbonic  oxide  require  i 
litre  of  oxygen  for  its  complete  combustion,  and  2  litres  of 
carbonic  anhydride  are  produced  : 

CO    +  O      =      C02 

There  are  several  other  ways  of  preparing  carbonic  oxide. 
The  best  of  these  consists  in  drying  the  yellow  salt  known 
as  potassic  ferrocyanide,  K4FeC6N6,  3H2O  (prussiate  of 
potash),  till  it  crumbles  down  to  a  white  powder. 

Exp.  84. — Mix  5  grams  of  this  dry  powder  with  50  c.  c.  of  oil 
of  vitriol  in  a  Florence  flask  ;  adjust  a  cork  and  a  wide  bent  tube 
to  the  mouth  of  the  flask,  and  heat  the  mixture.  When  the  heat 
reaches  a  certain  point,  the  gas  will  come  off  very  quickly. 

In  this  experiment  the  decomposition  is  complicated,*  but 
the  result  is,  that  the  whole  of  the  carbon  of  the  salt  comes 
off  as  pure  carbonic  oxide,  while  the  whole  of  its  nitrogen 
remains  behind  as  an  ammonium  salt  with  the  acid  em- 
ployed. 

Another  plan  commonly  practised  for  obtaining  carbonic 
oxide  is  to  heat  crystals  of  oxalic  acid  with  about  10  times 
their  weight  of  oil  of  vitriol ;  but  in  this  case  the  carbonic 
oxide  is  mixed  with  an  equal  volume  of  carbonic  anhydride : 

Oxalic  Acid  Water  Carbonic  Anhydride  Carbonic  Oxide 

H,C,04      -      H,0     -  CO,  +  CO 

In  this  process  the  oxalic  acid  is  deprived  of  the  elements 

*  Potassic  w-fi.1  Sulphuric 

Ferrocyanide  Acid 

K4FeC6N6     +     6H2O     +     6H2SO4 

Carbonic  Potassic  Ferrous  Ammonic 

Oxide  Sulphate  Sulphate  Sulphate 

~      6CO     +     2KtS04     +     FeS04     + 


Q6  Properties  of  Carbonic  Oxide. 

of'  water  by  the  sulphuric  acid,  and  the  remaining  carbon 
and  oxygen  pass  off  in  the  form  of  equal  measures  of  the 
two  gases. 

The  carbonic  anhydride  may  be  removed  by  causing  the 
mixture  of  gases  to  pass  through  a  solution  of  caustic  soda ; 
and  the  apparatus  may  be  arranged  as  shown  in  Fig.  28,  in 
which  the  gas  generated  in  the  flask  A  is  transmitted  through 


the  tube  B,  which  passes  loosely  through  the  wider  tube  c 
below  the  surface  of  a  solution  of  soda  contained  in  the 
bottle  D.  From  this  bottle  the  gas  passes  off,  by  a  tube  the 
end  of  which  is  above  the  solution,  into  the  jar  E  standing 
in  the  pneumatic  trough. 

Carbonic  oxide  is  a  gas  without  colour,  but  with  a  faint 
oppressive  odour.  It  is  very  poisonous  when  breathed,  so 
small  a  quantity  as  i  measure  of  the  gas  in  100  of  air 
speedily  producing  a  peculiar  sensation  of  oppression  and 
tightness  of  the  head.  The  fumes  of  burning  charcoal  owe 
their  most  active  poisonous  property  to  the  presence  of  car- 
bonic oxide,  which  is  always  largely  mixed  with  carbonic 
anhydride  in  the  products  of  a  slowly-burning  charcoal  fire. 
This  gas  has  not  been  liquefied,  either  by  cold  or  pressure. 
It  is  but  slightly  soluble,  100  c.  c.  of  water  dissolving  about 
2 -4  c.  c.  of  the  gas.  A  solution  of  cupreous  chloride  (CuCl) 
in  hydrochloric  acid  dissolves  carbonic  oxide  gas  slowly  if 


On  Crystallisation.  97 

agitated  with  it,  but  the  gas  is  not  soluble  in  a  solution  of 
potash. 

(20)  Classification  of  Crystals. — We  have  had  occasion  to 
allude  to  the  crystalline  form  of  the  diamond  and  some  other 
substances,  and  different  varieties  of  crystals  will  continually 
need  notice.  It  will  therefore  be  necessary  to  acquire  some 
general  notions  of  what  is  meant  when  crystals  are  spoken 
of,  how  their  different  varieties  are  designated,  and  what  are 
the  principles  on  which  their  different  forms  are  classified. 

Exp.  85. — Dissolve  250  grams  of  nitre  in  half  a  litre  of 
boiling  water,  and  allow  the  solution  to  cool  slowly  in  a  basin. 
Six-sided  prisms  will  gradually  be  formed  in  the  liquid,  owing 
to  the  separation  of  part  of  the  salt. 

Exp.  86. — Dissolve  some  common  salt  by  grinding  it  with 
about  twice  its  weight  of  water  in  a  mortar.  Pour  off  the  clear 
liquid,  and  set  it  aside  for  several  days  in  a  soup  plate  or  other 
shallow  vessel :  the  water  will  gradually  evaporate,  and  little 
cubes  of  salt  will  be  formed. 

Exp.  87. — Prepare  in  like  manner  a  solution  of  alum,  and 
leave  it  to  evaporate  slowly,  when  transparent  octahedra  will  be 
obtained. 

In  most  cases,  where  solid  bodies  are  allowed  to  separate 
undisturbed  from  their  solutions,  they  are  found  to  assume 
the  form  of  some  regular  geometrical  solid,  bounded  by  flat 
faces,  called  planes.  Each  substance  has  its  own  peculiar 
form,  and  the  regular  geometrical  solids  thus  obtained  are 
called  crystals.  By  these  differences  in  form  many  substances 
may  be  at  once  distinguished  from  each  other.  The  process 
of  crystallisation  is  commonly  used  as  a  means  of  freeing 
salts  from  small  quantities  of  foreign  admixture ;  as,  for 
instance,  for  separating  nitre  from  small  quantities  of  com- 
mon salt.  The  impure  nitre  is  dissolved  in  hot  water,  and 
the  nitre  as  it  cools  crystallises,  whilst  the  liquid,  or  mother 
liquor,  retains  in  solution  the  small  proportion  of  common  salt. 

The  principle  upon  which  the  classification  of  crystals  is 
founded  is  the  symmetry  of  their  form.  By  symmetry  is 
oieint  a  complex  uniformity  of  figure;  in  other  words,  a 

H 


98  Axes  of  Crystals. 

similar  arrangement  of  two  or  more  corresponding  forms 
round  a  common  centre.  This,  indeed,  is  the  general  law  of 
creation.  It  is  seen  in  the  correspondence  of  external  form 
of  the  two  sides  of  the  body  in  animals  ;  of  the  two  halves 
of  a  leaf  on  either  side  of  its  midrib  in  plants  ;  in  the  two 
halves  of  most  seeds ;  and  still  more  rigidly  in  the  constitu- 
tion of  every  crystal.  The  imaginary  line  round  which  the 
parts  of  a  crystal  are  symmetrically  disposed  is  called  the 
axis  of  symmetry,  or,  simply,  the  axis  of  a  crystal. 

Select  an  octahedral  crystal  of  alum,  and  place  it  with  one 
of  its  angles  uppermost ;  an  imaginary  line,  a  a,  Fig.  290,  pass- 
ing through  the  middle  of  the  crystal  to 
the  opposite  angle  is  an  axis  of  the  crys- 
tal. Each  end  of  this  axis  is  formed  by 
the  meeting  of  four  sides  or  planes  of 
the  crystal.  Every  one  of  these  sides  is 
similar  to  its  fellows,  and  each  is  in- 
clined to  the  axis  at  an  equal  angle. 
Each  of  the  four  faces  therefore  is  sym- 
metrically disposed  around  the  axis. 
If  any  internal  force  act  upon  the  particles  during  the 
formation  of  the  crystal,  so  as  to  produce  a  bevelling  of  one 
of  the  edges  of  any  one  of  these  planes,  the  same  cause 
will  act  upon  the  other  corresponding  edges,  and  will  pro- 
duce a  corresponding  modification  of  a  symmetrical  character 
upon  each  of  the  other  corresponding  edges.  This  regu- 
larity is  often  interfered  with  mechanically,  as  when  many 
crystals  are  formed  in  the  same  mass,  or  by  the  accident  of 
its  position  during  its  formation. 

In  describing  crystals,  several  of  these  imaginary  lines  are 
supposed  to  exist,  around  which  their  faces  are  arranged. 
Generally  speaking,  these  axes  may  be  reduced  to  three,  all 
of  which  intersect  each  other  in  the  centre  of  the  figure. 

For  the  purpose  of  making  the  direction  of  these  axes 
more  easily  understood,  let  a  piece  of  soap  be  cut  in  the 
form  of  a  cube,  or  figure  of  6  equal  square  sides,  eaofc  of 


Cleavage  of  Crystals. 


99 


Fig.  290. 


which  is  6  or  8  centimetres  long ;  through  the  middle  of  one 

of  its  sides  thrust  a  piece  of  wire  1-8-  centimetres  long,  so 

that  it  shall  pass  out  in  the  middle 

of  the  opposite   side,   and  project 

equally  on  either  side,  as  shown  at 

a  a,  Fig.  290;  do  the  same  through 

two   of   the  other  sides,  as  at  bb. 

These  two  wires  will  represent  the 

direction  of  two  out  of  the  three  axes 

of  the  cube  which  cross  each  other 

at  right  angles  at  its  centre.     Now 

repeat  the  process  on  the  remaining 

two  sides.     The  third  axis  of  the  cube  will  be  represented  by 

this  third  wire,  which  will  be  at  right  angles  to  both  the  others, 

Fig.  30.  Fig.  31.  Fig.  32. 


Fig.  33- 


Twist  a  piece  of  thread  round  the  end  of  one  of  the  wires,,  and 
connect  each  point  of  the  wires  in  succession  with  each  of 
the  four  points  nearest  to  it,  stretching  the 
thread  across  from  one  to  the  other.  An 
outline  of  the  regular  octahedron  will  thus 
be  formed.  Take  another  cube  of  soap, 
and  pare  off  each  of  its  8  corners,  as  at 
00,  Fig.  30,  by  a  plane  inclined  equally 
to  each  of  the  three  adjacent  faces  of  the 
cube.  If  these  new  faces  be  gradually 
enlarged  by  continuing  to  pare  away  the  corners,  as  shown  in 
the  Figs.  31  and  32,  the  cube  will  by  degrees  be  converted 
into  the  octahedron  (Fig.  36),  an  8-sided  solid,  in  which  the 
three  axes  of  the  cube,  a  a,  a  a,  a  a,  end  in  the  six  solid  angles 
of  the  octahedron.  If  in  another  cube  of  soap  the  1 2  edges 

H  2 


-v  

-*V 

100 


First  and  Second  Systems. 


of  the  cube  be  pared  off  so  as  to  form  12  planes,  £,  3,  Fig.  33, 
sloped  equally  towards  the  adjacent  faces,  the  cube  will 
gradually  be  converted  into  a  regular  12 -sided  figure,  the 
rhombic  dodecahedron  (Fig.  34),  which  is  also  symmetrically 


Fig.  35- 


Fig.  36. 


•*an 


arranged  around  the  three  axes  of  the  cube  (Fig.  35).  These 
three  forms,  the  cube,  the  octahedron,  and  the  rhombic 
dodecahedron,  being  formed  around  a  similar  set  of  axes, 
are  said  to  belong  to  the  same  system  of  crystals ;  and 
this  particular  system  is  called  the  regular  or  cubic  system. 
All  the  different  known  forms  of  crystals  have  been  ar- 
ranged in  one  or  other  of  six  such  systems  or  classes, 
viz.: — 

i  st.  The  regular  or  cubic,  distinguished  by  possessing  three 
axes  equal  in  length,  crossing  each  other  at  right  angles. 
Common  salt  and  fluor  spar,  which  crystallise  in  cubes,  alum 
in  octahedra,  and  garnet  in  the  rhombic  dodecahedron,  are 
examples  of  this  class. 

2nd.  The  square  prismatic  or  pyramidal. — In  this  system 


Fig.  37- 


Fig.  39- 


Third  System. 


101 


there  are  also  three  axes,  which  cross  each  other  at  right 
angles ;  two  of  these  axes  are  equal,  but  the  third  or  prin- 
cipal axis  is  either  longer  or  shorter  than  the  others.  The 
forms  of  this  system  are  either  (i)  the  octahedron  (Fig.  37), 


Fig.  390. 


Fig.  40. 


Fig.  41. 


such  as  potassic  ferrocyanide,  which  sometimes  loses  the 
pointed  terminations  and  becomes  shortened  into  the  form 
of  a  table,  or  flat,  plate  ;  or  (2)  the  square  prism,  sometimes 
ending  in  the  faces  of  the  octahedron,  as  tin-stone  (Fig.  39*2). 
The  base  of  the  octahedron  is  shown  in  Fig.  38,  with  its  two 
equal  axes,  A  A,  A  A,  terminating  in  the  angles ;  but  there  are 
octahedra  in  which  the  two  axes  terminate  in  the  middle  of 
the  sides,  as  shown  in  Figs.  39,  40,  in  which,  in  Fig.  39,  the 
principal  axis,  c  c,  is  seen  intersecting  one  of  the  others. 

3rd.  The  rhombohedral  or  hexagonal  system. — There  are 
four  axes  in  this  system :  three  of  these  are  in  the  same  plane 
or  flat  surface ;  they  are  equal  in  length,  and  cross  each  other 
at  angles  of  60°,  as  shown  in  Fig.  41 ;  while  the  fourth  or 


Fig.  42. 


Fig.  43- 


Fig.  44. 


principal  axis  crosses  the  other  three  at  right  angles,  and 

ay  be  either  longer  or  shorter  than  they.     The  six-sided 

prism,  like  beryl  (Fig.  42),  and  the  rhombohedron,  such  as 

Iceland  spar  (Fig.  43),  are  the  most  important  forms,  some- 


102 


Fourth  and  Fifth  Systems. 


Fig.  45- 


times  conjoined  with  the  double  six-sided  pyramid  which 
usually  terminates  the  crystals  of  quartz  (Fig.  44). 

4th.  The  prismatic  system. — In  this  there  are  three  axes, 
A  A,  B  B,  c  c,  all  unequal  in  length,  but  they  all  cross  each 

other    at     right 
angles.     Two  of 
them     form     a 
rhombic       base 
for  the  prism  or 
octahedron,     as 
shown  in  Figs.  45,  46,  47,  the 
dimensions  of  the  rhomboid 
varying  according  to  the  length 
of  each  pair  of  axes  included 
in  the  section. 

Fig.  48  represents  an  octahedron  of  this  system,  to  which 
sulphur  crystallised  in  the  cold  belongs.  Fig.  49  represents  a 
tabular  prism  of  this  class. 

5th.  The  obliqtie  system. — In  this  there  are  three  axes, 
which  may  all  differ  in  length ;  'two  of  them  cross  each 
other  obliquely,  as  is  shown  in  the  principal  section  of 
the  octahedron  (Fig.  51),  while  the  other  crosses  them 
both  perpendicularly,  as  shown  in  Fig.  52. 
The  octahedron  itself  is  seen  at  Fig.  50. 
The  principal  forms  are  the  oblique  rhombic 


Fig.  48. 
c 


prism,  a  modification  of  which  is  seen  at  Fig.  520.  Sulphur 
crystallised  after  fusion,  sodic  sulphate,  and  borax  belong  to 
this  system. 


Sixth  System — Isomorphism. 


103 


6th.  The  doubly  oblique  system.  This  is  the  most  com- 
plicated of  the  whole  series.  The  three  axes  may  all  differ 
in  length,  and  they  cross  each  other  obliquely.  Cupric 


Fig.  52. 


Fig.  5  2  a. 


sulphate  and  bismuth  nitrate  offer  good  examples  of 
the  doubly  oblique  prism,  one  modification  of  which  is  shown 
in  Fig.  53,  while  the  octahedron  is  seen  in  Fig.  54. 

Fig.  53- 


Inorganic  bodies  which  are  destitute  of  crystalline  form 
are  said  to  be  amorphous.  When,  like  carbon,  they  crystallise 
in  forms  which  belong  to  two  distinct  crystalline  systems, 
they  are  said  to  be  dimorphous ;  and  when  with  a  similar 
chemical  composition  they  crystallise  in  similar  forms,  as  is 
the  case  with  the  arseniates  and  phosphates  of  the  same 
metal,  or  the  seleniates  and  sulphates  of  the  same  metal, 
they  are  said  to  be  isomorphous. 

NOTE. — A  prism  is  a  solid,  the  lateral  edges  of  which  are  parallel, 
and  the  terminal  planes  of  which  are  also  parallel.  Prisms  which  stand 
perpendicularly  when  resting  on  their  bases  are  called  right  prisms ;  those 
which  incline  from  the  perpendicular  are  called  oblique  prisms.  When 
the  base  is  a  rhomb,  or  a  rhomboid,  it  is  called  a  rhombic  prism ;  and 
a  rhombohedron  is  a  six-sided  solid,  all  the  sides  of  which  are  formed 
by  rhombs,  a  rhomb  being  a  plane  figure  with  four  equal  parallel  sides, 
but  the  angles  of  which  are  not  right  angles,  while  a  rhomboid  is  a 
similar  figure  in  which  one  pair  of  sides  is  longer  than  the  other  pair. 


IO4 


CHAPTER  V. 

OXIDES   OF    NITROGEN — NITRIC   ACID AMMONIA. 

(21)  NITRIC  ACID:  Symb.  HNO3;  Atomic  Wt.  63;  Sp.gr. 
of  liquid,  1-52  ;  Boiling  Pt.  84-5°  C. ;  Freezing  Pt.  about 
-  40°  C. 

The  attraction  of  oxygen  for  nitrogen  is  but  feeble  ;  these 
gases  do  not  easily  combine  together,  and  they  remain  mixed 
together  without  change  and  under  great  variation  of  con- 
ditions in  atmospheric  air.  Nevertheless,  true  chemical  com- 
pounds may  be  formed  between  them,  differing  entirely  in 
properties  from  the  bland  mixture  which  we  breathe  at  every 
moment.  As  in  many  other  cases  where  the  attraction 
between  two  elements  is  weak,  nitrogen  forms  with  oxygen 
several  compounds,  not  fewer  than  five  being  known ;  they 
contain  i,  2,  3,  4,  and  5  volumes  of  oxygen  respectively, 
uniting  in  each  case  with  2  volumes  of  nitrogen. 

These  compounds  have  been  named — 

1.  Nitrous  Oxide     .        .        .     NaO 

2.  Nitric  Oxide        .        .        .     N4Oa    or  NO 

3.  Nitrous  Anhydride      .         .     N4O3 

4.  Nitrogen  Peroxide       .        .     NaO4   or  NOa 

5.  Nitric  Anhydride        .         .     NaO5 

The  third  of  these  oxides,  when  dissolved  in  water,  fur 
nishes  nitrous  acid  (HNO2),  for 

H20  +  N203     =     2HN02; 

and  the  fifth  yields  nitric  acid  (HNO3),  since 

H2O  +  N2O5     =     2HNO3. 

Nitric  acid  is  one  of  the  most  important  acids  known.  It 
was  formerly  called  aqua-fortis  (strong  water),  from  its  cor- 
rosive action  and  power  of  dissolving  the  metals. 

Traces  of  nitric  acid  are  always  formed  when  a  discharge 
of  electricity  passes  through  moist  air,  so  that  rain  water 
generally  contains  a  trace  of  this  acid,  owing  to  the  action 
of  lightning  or  atmospheric  electricity.  But  in  tropical 


Distillation  of  Nitric  Acid. 


105 


climates,  particularly  in  some  districts  of  India,  potassic 
nitrate,  and  in  Chili  sodic  nitrate,  is  found  as  an  efflorescence 
upon  the  surface  of  the  soil.  It  is  from  one  of  these  salts 
that  nitric  acid  is  extracted  for  use  in  the  arts.  The  opera- 
tion may  be  conducted  on  a  small  scale  as  follows : — 

Exp.  88. — In  a  retort,  a,  Fig.  55,  which  will  hold  2  litres  place 
half  a  kilogram  of  sodic  nitrate,*  and  pour  over  it  an  equal 
weight  of  concentrated  sulphuric  acid.  Adjust  the  retort  to  a 
Liebig's  condenser  (Fig.  1 1),  or  even  to  a  long  straight  tube,  as 
shown  at  b,  and  cover  the  upper  part  of  the  retort  with  a  tinplate 

Fig-  55- 


cap,  c,  for  the  purpose  of  keeping  the  body  of  the  retort  hot, 
and  distil  the  mixture  carefully  over  an  Argand  gas-burner, 
collecting  the  intensely  corrosive  acid  liquid  in  a  flask  cooled  by 
immersion  in  a  pan  of  water.  This  experiment  is  best  made  in  an 
outhouse  where  there  is  a  free  current  of  air.  Red  fumes  come 
off,  and  a  straw-coloured  liquid  distils  over,  which  is  concentrated 
nitric  acid,  or  hydric  nitrate,  as  it  is  now  sometimes  called. 

In  this  distillation  the  kind  of  change   called   '  double 

*  In  making  the  acid,  smaller  quantities  may  be  used,  and  saltpetre 
or  nitre  (the  potassic  nitrate,  KNO3)  may  be  employed  instead  of  sodic 
nitrate. 


io6 


Decomposition  of  Sodic  Nitrate. 


decomposition  '  takes  place  ;  part  of  the  hydrogen  of  the 
sulphuric  acid  changes  place  with  a  corresponding  amount 
of  the  sodium  of  the  sodic  nitrate,  forming  hydric  sodic 
sulphate,  which,  as  it  is  not  volatile,  remains  in  the  retori, 
while  the  more  volatile  nitric  acid  distils  over  when  heated. 
The  decomposition  may  be  thus  represented  : 

Sulphuric  Acid  Sodic  Nitrate  Hydric  Sodic  Sulphate  Nitric  Acid 

HaSO4          +       NaNO3       =         NaHSO4         +       HNO3 
1x2  +  32+16x4     23+14+16x3     23  +  1+32  +  16x4     i  +  i4+i6x; 

98  85  120  63 

This  plan  of  obtaining  nitric  acid  from  one  of  its  metallic 
salts  affords  a  good  instance  of  the  method  adopted  generally 
when  volatile  acids  which  can  be  distilled  without  suffering 
decomposition  are  required.  The  weaker  and  more  volatile 
acid  is  in  such  cases  displaced,  like  the  nitric,  by  the  stronger 
and  less  volatile  acid,  such  as  the  sulphuric;  and  in  the 
process  the  hydrogen  of  the  stronger  acid  changes  place 
with  the  metal  contained  in  the  salt  of  the  acid  sought. 
The  ordinary  acids,  it  must  be  remembered,  are  always  salts 
of  hydrogen.  • 

When  nitric  acid  is  distilled  in  glass  vessels,  the  quantity 
of  sulphuric  acid  used  is  double  that  required  by  the  manu- 
facturer, who  employs  a  large  iron  cylinder,  the  upper  part 
of  which  is  lined  with  fire-clay  to  protect  it  from  the  action 
of  the  acid  vapours ;  but  it  requires  a  higher  heat  to  drive 
off  the  last  portions  of  the  nitric  acid. 

In  fact,  sulphuric  acid  forms  two  different  salts  with 
sodium,  one  of  which  is  an  acid  sulphate,  and  the  other  a 
neutral  sulphate ;  the  neutral  sulphate  containing  twice  as 
much  sodium  as  the  other.  The  acid  sulphate,  or  hydric 
sodic  sulphate  (NaHSO4)  is  very  soluble  and  readily  fusible, 
so  that  it  can  be  extracted  from  the  glass  retort  without  risk ; 
while  the  neutral  sulphate  (Na2SO4)  is  less  soluble,  and 
cannot  be  melted  in  glass  vessels. 

When  sodic  nitrate  and  sulphuric  acid  are  mixed  in  the 


Properties  of  Nitric  A  cid.  1 07 

proportion  of  equal  weights,  the  whole  of  the  nitre  is  decom- 
posed in  one  stage ;  the  acid  salt  only  is  obtained,  and  nitric 
acid  comes  over  at  a  low  temperature;  half  the  hydrogen 
only  of  the  sulphuric  acid  being  displaced  by  sodium.  The 
change  is  represented  by  the  equation  already  given — 
H2SO4  +  NaN03  =  NaHSO4  +  HNO3. 

But  if  the  nitrate  be  mixed  with  half  its  weight  only  of  sul- 
phuric acid,  the  decomposition  takes  place  in  two  stages, 
instead  of  in  one.  In  the  first  of  these,  half  the  nitre  only  is 
decomposed,  hydric  sodic  sulphate  being  produced  at  first, 
as  before,  and  a  gentle  heat  is  sufficient  to  distil  over  this 
first  half  of  the  nitric  acid — 
H2SO4  +  2NaNO3  =  NaHSO4  +  HNO3  +  NaNO3. 

As  soon  as  the  first  half  of  the  nitric  acid  has  come  over,  the 
heat  must  be  increased ;  the  acid  sulphate  will  then  begin  to 
act  upon  the  undecomposed  nitre;  the  second  half  of  the 
nitric  acid  is  now  formed,  but  is  partly  decomposed,  par- 
ticularly towards  the  end  of  the  process.  The  whole  of  the 
sodium  remains  in  the  retort  in  the  form  of  disodic  sulphate, 
or  the  neutral  sulphate.  This  second  stage  of  the  distillation 
may  be  represented  by  the  following  equation — 

Sodic  Nitrate         Hydric  Sodic  Sulphate  Nitric  Acid         Sodic  Sulphate 

NaNO3     +         NaHSO4  =     HNO3     +     Na3SO4. 

The  acid  which  is  distilled  in  this  way  has  a  yellow  colour, 
owing  to  the  presence  of  one  of  the  lower  oxides  of  nitrogen 
in  solution ;  but  the  pure  acid  is  quite  colourless.  Its  exact 
analysis  cannot  easily  be  made.  It  is  very  easily  decom- 
posed. The  sun's  light  causes  it  to  change,  and  give  off 
oxygen  gas,  while  the  acid  becomes  yellow  or. brown.  It  is 
a  fuming  intensely  corrosive  liquid,  which  stains  the  skin  of 
a  permanent  yellow.  It  freezes  at  about  —  40°  C.,  and 
begins  to  boil  at  85-5°  C. 

Nitric  acid  is  a  powerful  oxidising  agent. 

Exp.  89. — Place  a  little  warm  powdered  charcoal  in  a  small 
saucer,  and  pour  over  it  about  a  teaspoonful  of  the  strongest 


io8  Action  of  Nitric  Acid  on  Metals. 

nitric  acid  from  a^  test-tube  fastened  to  the  end  of  a  stick  :  the 
charcoal  will  burn  with  sparks. 

Exp.  90. — Fasten  a  test-tube  to  the  end  of  a  stick,  and  mix  in 
the  tube  about  2  c.  c.  of  nitric  acid  with  an  equal  measure  of 
concentrated  sulphuric  acid.  Place  about  2  c.  c.  of  oil  of  tur- 
pentine in  a  small  cup,  under  the  chimney,  and  pour  the  acid 
into  the  turpentine  at  arm's  length  :  the  mixture  will  burst  into 
a  blaze. 

Exp.  91. — Mix  the  strong  acid  with  about  an  equal  bulk  of 
water  ;  pour  2  or  3  c.  c.  of  the  mixture  upon  a  few  copper  turn- 
ings :  dense  red  fumes  will  be  given  off,  and  the  copper  will  be 
dissolved,  forming  a  blue  solution  of  cupric  nitrate. 

Iron  filings,  tinfoil,  and  many  other  metals,  when  in  a 
divided  state,  are  acted  upon  by  nitric  acid  with  almost  equal 
violence  ;  indeed,  this  acid  dissolves  or  attacks  nearly  all  the 
common  metals,  except  gold  and  platinum.  The  mode  of 
its  action  varies  according  to  the  temperature  and  the 
degree  of  its  dilution  with  water.  Usually  it  acts  most 
powerfully  when  of  a  sp.  gr.  between  1*25  and  1*35,  or  when 
the  strong  acid  is  mixed  with  from  two-thirds  of  its  bulk  to 
an  equal  bulk  of  water. 

Action  of  Metals  on  Acids. — When  the  common  metals 
are  presented  to  any  of  the  stronger  acids  a  brisk  action 
frequently  occurs,  accompanied  with  escape  of  gas.  In  all 
but  a  few  cases  the  first  action  of  the  metal  consists  in  set- 
ting free  the  hydrogen  of  the  acid,  which  is. replaced  by  the 
equivalent  quantity  of  the  metal,  thus  forming  a  salt ;  for 
example,  zinc  and  sulphuric  acid  yield  hydrogen  and  zincic 
sulphate—  Zn  +  H2SO4  =  H2  +  ZnSO4. 

It  is  not  always,  however,  that  the  hydrogen  thus  displaced 
is  evolved  as  such ;  if  the  conditions  be  favourable  it  often 
reacts,  at  the  moment  of  liberation,  on  the  excess  of  acid 
present ;  thus,  by  the  action  of  copper  on  strong  sulphuric 
acid,  which  only  takes  place  on  heating,  no  hydrogen  is 
evolved,  but  cupric  sulphate,  water,  and  sulphurous  an- 
hydride are  formed — 

Cu  +  2H2SO4     =     CuSO4  +  SO2  +   2H2O. 


Nitric  A  cid — Nitrates.  1 09 

This  reaction  doubtless  occurs  by  two  stages  :  at  the  first 
cupric  sulphate  is  formed  and  hydrogen  liberated — 

Cu  +  H2SO4     =     CuSO4  +  H2, 

but  this  hydrogen,  which  has  no  appreciable  reaction  on  cold 
sulphuric  acid,  is  able  to  attack  the  strongly  heated  acid,  and 
at  once  deprives  it  of  a  portion  of  its  oxygen,  reducing  it  to 
sulphurous  acid,  which  further  splits  up  into  the  anhydride 
and  water : 

H2SO4  +  H2     =     H2SO3;  H2SO3     =     H2O  +  SO2. 

Nitric  acid  being  a  powerful  oxidising  agent,  i.e.  a  body 
which  readily  gives  up  oxygen,  never  yields  free  hydrogen 
when  acted  upon  by  metals,  but  is  more  or  less  reduced 
(deprived  of  oxygen)  by  the  nascent  hydrogen. 

Exp.  92. — Act  upon  zinc  or  iron  with  dilute  sulphuric  acid 
and  collect  the  gas  evolved ;  it  will  burn  on  the  application  of 
flame,  and  is,  in  fact,  hydrogen.  Now  add,  drop  by  drop, 
dilute  nitric  acid  :  the  evolution  of  gas  ceases,  but  the  metal 
continues  to  dissolve  ;  the  hydrogen  combines  with  the  elements 
of  nitric  acid  to  form  water  and  ammonia.  The  latter  may  be 
detected  at  the  close  of  the  experiment  by  adding  sodic  hydrate 
to  alkaline  reaction,  and  heating,  when  the  smell  of  ammonia 
will  be  apparent. 

The  successive  reactions  which  may  be  supposed  to  occur 
in  the  production  of  nitric  oxide,  for  example,  by  the  action 
of  copper,  or  mercury,  on  nitric  acid  will  be  evident  from 
tie  following  equations  : 

1.  Cu    +    2HN03     =     Cu2NO3  +  H2 

2.  3H2  +    2HNO3     =       2NO        +  4H2O. 

Collecting  these  in  one  we  obtain  as  expression  of  the 
entire  reaction — 

Copper        Nitric  Acid        Nitric  Oxide    Cupric  Nitrate          Water 

3Cu   +   8HNO3     =     2NO 


HO  Nitrous  Oxide. 

but  it  is  evident  that  this  equation  affords  no  insight  into 
the  course  of  the  reaction. 

The  primary  reaction  of  a  metal  on  an  acid  may  be  con- 
sidered identical  in  all  cases,  and  to  consist  in  the  formation 
of  the  corresponding  salt  and  hydrogen  ;  the  secondary  re- 
actions which  occur,  which  generally  consist  in  the  reduc- 
tion of  a  portion  of  the  acid,  depend  entirely  on  the  nature 
both  of  the  acid  and  the  metal  employed,  on  the  state  of 
concentration  of  the  acid,  and  on  the  temperature  at  which 
the  reaction  takes  place.  Thus  by  the  action  of  various 
metals  on  nitric  acid  we  may  obtain  at  will  either  ammonia, 
nitrogen,  nitrous  oxide,  nitric  oxide,  or  nitrogen  peroxide. 

By  the  action  of  metallic  oxides  on  nitric  acid  the  cor- 
responding nitrates  and  water  are  formed — 

CuO   +  2HNO3     =     Cu2NO3  +   H2O. 

The  nitrates  are  all  freely  soluble  in  water ;  when  heated 
they  decompose,  leaving  a  residue  of  the  oxide  of  the  metal 
and  giving  off  oxides  of  nitrogen  and  oxygen  ;  when  thrown 
on  red-hot  charcoal  deflagration  (or  burning  with  violence) 
ensues  owing  to  the  rapidity  with  which  they  give  up  oxygen 
to  the  burning  charcoal.* 

(22)  Other  Oxides  of  Nitrogen. — NITROUS  OXIDE  (or 
Nitrogen  Protoxide)  :  Symb.  N2O;  Atom,  and  MoL  Wt.  44; 
Mol.  Vol.  m  ;  Sp.  Gr.  1-527  ;  Rel.  Wt.  22. 

If  pure  nitric  acid  be  neutralised  by  ammonium  carbonate, 
and  the  solution  be  evaporated  to  dryness,  a  solid  white  salt 
is  left,  ammonium  nitrate  (H4N,  NO3). 

Exp.  96. — Heat  a  small  quantity  of  this  salt  in  a  test-tube:  it 
will  melt,  and,  if  heated  more  strongly,  will  appear  to  boil,  giving 
off  a  considerable  quantity  of  steam,  and  will  at  length  be 
wholly  dissipated.  If  a  cork  and  bent  tube  be  adjusted  to  the 
mouth  of  the  test-tube,  a  gas  may  be  collected  over  warm  water. 

The  ammonium  nitrate  is  entirely  decomposed  by  heat 
into  water  and  nitrous  oxide  gas,  H4N,  NO3  becoming 

*  For  detection  of  Nitric  Acid,  see  Appendix. 


Properties  of  Nitrons  Oxide.  II  i 

2H2O  +  N2O.  Nitrous  oxide  gas  is  colourless  and  trans- 
parent, and  has  a  faint  sweetish  smell  and  taste.  It  is  unfit 
for  the  support  of  life,  but  may  be  breathed  for  a  time  ;  and 
it  exerts  a  remarkable  action  upon  the  brain  and  nerves. 
If  respired  in  a  pure  state,  it  produces  transient  insensibility, 
and  is  in  consequence  sometimes  administered  to  deaden 
the  pain  in  surgical  operations.  If  it  be  mixed  with  air,  and 
breathed  for  a  few  minutes,  it  occasions  a  peculiar  kind  of 
intoxication,  often  attended  with  uncontrollable  laughter  : 
this  has  given  to  the  compound  its  popular  name  of  laughing 
gas ;  the  effect  soon  passes  off. 

Many  bodies  burn  in  nitrous  oxide  nearly  as  brightly  as 
in  oxygen  gas,  the  nitrous  oxide  being  decomposed  into  its 
elements  by  the  burning  body. 

Exp.  97. — Fill  a  small  jar  with  the  gas,  and  thrust  into  it  a 
splinter  of  wood  of  which  the  end  is  still  glowing  brightly  :  it 
will  burst  into  flame. 

Exp.  98. — Place  some  sulphur  in  a  deflagrating  spoon ;  kindle 
the  sulphur,  and  when  burning  briskly  introduce  it  into  the  gas  : 
it  will  burn  with  a  pale  rose-coloured  flame. 

Exp.  99. — Half  fill  a  test-tube  with  gas,  over  water.  Close 
the  tube  under  water  firmly  with  the  thumb,  and  then  agitate 
the  water  and  gas  together.  On  removing  the  thumb  under 
water,  a  considerable  rush  of  water  into  the  tube  will  occur,  as 
the  gas  is  soluble  in  about  its  own  volume  of  cold  water.  By 
this  circumstance  the  gas  is  easily  distinguished  from  oxygen. 

Nitrous  oxide  contains  its  own  volume  of  nitrogen  united 
with  half  its  volume  of  oxygen,  the  three  measures  which 
the  two  gases  occupied  when  separate  becoming  condensed 
into  two  measures  by  combining — 

If  the  gas  be  mixed  with  its  own  bulk  of  hydrogen  in  a 
eudiometer,  and  the  electric  spark  be  passed,  an  explosion 
will  occur,  the  bulk  of  the  gas  will  be  reduced  to  exactly  one- 
half,  a  few  drops  of  water  will  be  formed,  and  pure  nitrogen 
will  be  left  equal  in  bulk  to  the  nitrous  oxide  employed, 
N2O  +  H2  becoming  N2  4-  H2O. 


112  Properties  of  Nitric  Oxide. 

NITRIC  OXIDE  :  Symb.  NO  ;  Atomic  and  MoL  Wt.  30 ; 
Sp.  Gr.  1-039;  Rel-  Wt.i$\  Atomic  and Mol.  Vol.  £ 

Exp.  100. — Dilute  nitric  acid  with  water  until  it  becomes  of 
the  sp.  gr.  1*2,  and  pour  about  60  cub.  centim.  of  it  upon  15  grams 
of  copper  clippings,  contained  in  a  retort  :  the  retort  becomes 
quickly  filled  with  red  fumes,  and  a  colourless  gas  may  be  col- 
lected over  water. 

In  this  experiment  3  molecules  of  copper  and  8  of  nitric 
acid  being  concerned, 'whilst  as  the  result,  3  molecules  of 
cupric  nitrate,  2  of  nitric  oxide,  and  4  of  water  are  formed, 
as  shown  in  the  equation  : 

3Cu  +   8HNO3     =     3(Cu2NO3)   -f   2NO   +  4H2O. 

Other  metals,  such  as  mercury,  may  be  substituted  for 
copper  in  this  reaction,  and  the  gas  will  still  be  formed. 

Nitric  oxide  has  a  strong  disagreeable  odour  ;  it  cannot  be 
breathed,  even  in  very  small  quantity,  without  producing  an 
instant  feeling  of  suffocation.  It  is  very  slightly  soluble  in 
water ;  but  its  most  remarkable  property  is  its  strong  ten- 
dency to  combine  with  oxygen. 

Exp.  101. — Allow  a  bubble  or  two  of  the  colourless  gas  to 
escape  into  the  air  :  dense  brownish-red  fumes  are  immediately 
formed. 

These  fumes  are  always  produced  when  the  gas  is  first 
prepared  in  the  flask,  owing  to  its  action  on  the  oxygen  of 
the  air  contained  in  it ;  they  consist  of  a  mixture  of  nitrous 
anhydride  and  of  nitrogen  peroxide,  and  are  freely  soluble  in 
water,  with  which  they  form  an  acid  liquid.  This  change  of 
colour,  produced  by  mixing  nitric  oxide  with  any  gas  con- 
taining free  oxygen,  often  affords  a  convenient  means  of 
detecting  small  quantities  of  oxygen  when  present  in  admix- 
ture with  other  gases,  such,  for  instance,  as  coal  gas. 

Exp.  1 02. — Fill  a  small  gas  jar  with  water  coloured  blue  by 
means  of  tincture  of  litmus,  and  pass  up  into  it  sufficient  nitric 
oxide  gas  to  fill  about  one-third  of  the  jar :  the  litmus  will  not 
change  in  colour.  Now  allow  a  few  bubbles  of  oxygen  to  pass 
up  into  the  nitric  oxide  :  deep  red  fumes  are  formed,  which  are 


Properties  of  Nitric  Oxide.  113 

quickly  dissolved,  and  the  blue  solution  becomes  red.  If  both 
the  oxygen  and  the  nitric  oxide  be  pure,  it  is  possible,  by  cautiously 
adding  the  oxygen,  to  cause  a  complete  absorption  of  both  gases. 

Many  combustible  bodies,  if  strongly  heated,  burn  well  in 
this  gas  ;  but  they  are  extinguished  if  not  heated  sufficiently 
to  begin  the  decomposition  of  the  gas  by  separating  the 
oxygen  from  the  nitrogen. 

Exp.  103. — Place  a  piece  of  dried  phosphorus  in  a  deflagrating 
spoon ;  kindle  it  with  a  hot  wire,  and  instantly  introduce  the 
phosphorus  into  a  jar  of  nitric  oxide  :  it  will  be  extinguished. 
Again  draw  it  out  into  the  air  :  it  will  burst  into  flame.  When 
burning  briskly,  again  put  it  into  the  jar  of  gas  :  it  will  now  burn 
nearly  as  vividly  as  in  pure  oxygen. 

Nitric  oxide,  in  contact  with  strong  nitric  acid,  is  im- 
mediately dissolved  by  it.  The  acid  becomes  first  yellow, 
and,  if  more  gas  be  added,  ultimately  green.  It  is  also  quickly 
dissolved  by  a  solution  of  ferrous  sulphate,  forming  an  intense 
olive-brown  liquid.  This  fact  is  often  taken  advantage  of  in 
testing  for  nitric  acid  or  for  nitrates  (Exp.  94). 

Nitric  oxide  contains  equal  bulks  of  its  component  gases  : 

1  litre  of  oxygen,  when  united  with  i  litre  of  nitrogen,  forms 

2  litres  of  nitric  oxide — 

[o]  +  [N]    =    |N;Q|, 

the  gases  having  united  without  undergoing  any  change  in 
bulk. 

If  potassium  or  tin  be  heated  in  the  gas  with  proper  care, 
the  metal  is  oxidized,  and  exactly  half  the  quantity  of  the  gas 

aployed  is  left.     This  residue  is  found  to  be  pure  nitrogen. 

Nitric  oxide  has  never  been  liquefied. 

Nitrous  Anhydride  (N2O3)  is  the  third  in  the  series  of  the 
oxides  of  nitrogen.  It  may  be  formed  by  mixing  4  measures 
of  nitric  oxide  with  i  measure  of  oxygen,  when  deep  red 
fumes  are  produced.  These  furnish  an  acid  liquid  when 
dissolved  in  water — 

N2O3   +    H2O     =     2HNO2. 

This  acid,  the  nitrous,  furnishes,  when  neutralised  by  bases, 

i 


114  Sources  of  A  mmonia. 

a  series  of  salts,  called  nitrites;  but  they  are  of  little  prac- 
tical importance. 

Nitrogen  Peroxide  (NO2  or  N2O4)  is  the  fourth  term  of 
this  remarkable  series  of  oxides.  It  is  most  easily  procured 
by  heating  lead  nitrate  in  a  glass  tube.  Deep  red  fumes  are 
given  off.  These  fumes  may,  at  a  low  temperature,  be  con- 
densed into  a  red  liquid,  and,  if  quite  free  from  water,  may 
even  be  obtained  in  crystals.  The  lead  nitrate  yields  oxygen 
and  lead  oxide,  as  well  as  nitrogen  peroxide,  2(Pb2NO3) 
becoming  2PbO  +  2N2O4  4-  O2.  (See  Appendix.) 

(23)  AMMONIA:  Symb.  H3N;  Atomic  Wt.  17;  Atomic 
andMol.  Vol.  fT]  ;  $t-  Gr.  0-59;  Rel.  Wt.  8-5. 

Nitrogen  and  hydrogen  cannot  be  made  to  unite  directly 
with  one  another,  but  they  combine  indirectly  under  various 
circumstances.  Only  one  compound  between  them  can  be 
isolated,  and  this  is  the  well-known  volatile  alkali  ammonia, 
or  hartshorn. 

Exp.  104, — Heat  a  tuft  of  hair  in  a  test-tube  :  it  will  become 
brown,  and  will  give  off  a  few  drops  of  an  offensively  smelling 
liquid,  which  will  immediately  turn  a  piece  of  reddened  litmus 
paper  blue,  owing  to  the  formation  of  ammonia. 

Shreds  of  bone,  of  ivory,  of  isinglass,  of  horn,  of  parchment, 
of  feathers,  or  of  silk,  and  most  other  animal  bodies  which 
contain  nitrogen,  when  thus  decomposed  by  heat,  give  off  a 
mixture  of  various  compounds  of  ill-odour,  among  which 
ammonia,  in  greater  or  less  quantity,  is  always  present. 

It  was  by  the  distillation  of  substances  of  this  kind  that 
ammonia  was  formerly  exclusively  procured,  but  now  it  is 
usually  obtained  from  the  waste  liquors  collected  during  the 
distillation  of  coal  in  the  manufacture  of  gas,  since  all  coal 
contains  small  quantities  of  compounds  of  nitrogen,  which 
furnish  ammonia  when  distilled  at  a  high  temperature. 

Whenever  moist  animal  substances  putrefy,  ammonia  is 
amongst  the  products.  It  is  abundant  in  stale  urine,  as  well 
as  in  guano,  which  is  the  decomposed  excrement  of  sea-fowl 


Preparation  of  A  mmonia*  115 

Exp.  105. — Mix  intimately  3  grams  of  fine  iron  filings  in  a 
mortar  with  0-2  gram  of  caustic  potash ;  introduce  the  mixture 
into  a  test-tube,  to  the  mouth  of  which  a  cork  and  a  bent  quill 
tube  are  attached.  Heat  the  mixture  in  a  Bunsen  gas  flame  : 
gas  will  escape,  and  may  be  collected  over  water  in  a  test-tube. 
It  burns  with  flame,  and  consists  of  hydrogen. 

At  a  high  temperature,  the  iron  displaces  hydrogen  from 
the  caustic  potash — 

5Fe  +   2KHO     =     s.FeO  +   K2O  +  H2. 

Exp.  1 06. — Mix  3  grams  of  iron  filings  intimately  with  o'2 
gram  of  nitre.  Heat  the  mixture  and  collect  the  gas  as  before  : 
it  will  not  burn,  does  not  render  limewater  milky,  and  is,  in  fact, 
nitrogen. 

The  iron  has  combined  with  the  oxygen  of  the  nitre,  potash 
is  formed,  and  nitrogen  is  liberated— 

5Fe  +   2KN03     =     sFeO  +  K2O   +   N2. 

Exp.  107. — Mix  6  grams  of  iron  filings  with  0-2  gram  of  caustic 
potash  and  0*2  gram  of  nitre,  and  heat  the  mixture  in  a  tube. 

The  gas  which  now  comes  off  has  the  pungent  smell  ot 
hartshorn ;  it  is  strongly  alkaline,  and  immediately  restores 
the  blue  colour  of  reddened  litmus.  In  the  reaction  which 
takes  place,  the  hydrogen  and  the  nitrogen,  at  the  moment 
that  each  is  set  free,  seize  one  upon  the  other,  and  ammonia 
is  formed — 
8Fe  +  6KHO  +  2KNO3  =  8FeO  +  4K2O  +  2H3N. 

Traces  of  ammonia  exist  in  the  atmosphere,  and  are 
brought  down  in  rain  and  dews  to  the  surface  of  the  earth. 
In  the  rusting  of  iron,  and  in  almost  every  other  process  of 
oxidation  when  moisture  is  present,  small  quantities  of 
ammonia  are  formed. 

The  common  mode  of  preparing  ammonia  for  experiment 
consists  in  heating  one  of  its  commercial  salts,  such  as  the 
sulphate  or  the  hydrochlorate,  with  a  strong  base,  like  lime. 
The  lime  combines  with  the  acid,  and  sets  the  ammonia  at 
liberty. 

I  2 


1 1 6  Properties  of  A  mmoniacal  Gas. 

Exp.  1 08. — Powder  finely  30  grams  of  sal  ammoniac,  and  mix 
it  with  20  grams  of  finely  powdered  lime  :  the  pungent  fumes  of 
Fig.  56.  ammonia  immediately  begin  to  escape. 

Place  the  mixture  in  a  flask  provided 
with  a  cork  and  a  drying  tube  filled 
with  quicklime  and  attached  to  a  bent 
tube  (Fig.  56).  Apply  a  gentle  heat, 
and  ammoniacal  gas  will  be  liberated. 
Ammoniacal  gas  is  very  soluble  in 
water,  which  at  1 5°  C.  dissolves  up- 
wards of  700  times  its  bulk  of  the 
gas  ;  so  that  it  cannot  be  collected 
over  water  without  being  absorbed. 
It  may,  however,  be  collected  over 
mercury. 

Exp.  109. — Fill  a  strong  test-tube 
with  mercury,  close  it  with  the  thumb, 
and  invert  it  in  a  small  basin  of 
mercury  over  the  end  of  the  gas-tube. 
Bubbles  of  gas  will  rise  in  the  tube,  and  will  displace  the 
mercury. 

Ammonia  is  much  lighter  than  the  air ;  and  this  fact  may 
be  taken  advantage  of  so  as  to  collect  it  in  a  flask  or  bottle, 
by  upward  displacement,  as  shown  in  Fig.  56 — 

2(H3N,  HC1)  +  CaO     =     CaCl2  +  H2O  +  2H3N. 

It  may  easily  be  ascertained  when  the  bottle  is  full  of  the 
gas  by  the  brown  colour  given  to  a  piece  of  dry  turmeric 
paper  brought  near  to  the  mouth. 

Ammonia  is  a  gas  which  has  no  colour ;  it  has  an  intensely 
pungent  odour,  and  brings  tears  into  the  eyes.  It  has  an 
acrid  taste.  It  is  a  strong  stimulant  to  the  nerves,  and,  in 
the  form  of  smelling-salts,  is  used  to  check  feelings  of  faint- 
ness.  It  is  powerfully  alkaline. 

Exp.  no. — Place  a  little  solution  of  litmus,  feebly  reddened 
by  the  addition  of  a  drop  or  two  of  any  acid,  in  a  basin  ;  carefully 
raise  the  flask  full  of  ammonia  gas  from  the  gas-delivering  tube  ; 
close  the  flask  with  the  thumb,  plunge  the  mouth  under  the 


Absorption  of  Ammonia.  117 

solution  of  litmus,  and  withdraw  the  thumb  :  the  liquid  will  rush 
rapidly  into  the  flask,  the  ammonia  gas  will  be  absorbed,  and 
the  red  liquid  will  become  blue. 

Ammonia  neutralises  the  most  powerful  acids,  and  forms 
with  them  an  important  series  of  salts,  some  of  which  will  be 
noticed  when  speaking  of  the  salts  of  the  metals  of  the 
alkalies.  Any  volatile  acid,  when  brought  into  an  atmo- 
sphere containing  ammonia,  produces  a  white  cloud,  by  com- 
bining with  the  ammonia  and  forming  a  white  solid  salt. 
This  property  is  often  used  to  detect  small  quantities  of 
ammonia. 

Exp.  in. — Mix  common  hydrochloric  acid  with  half  its  bulk 
of  water;  dip  a  glass  rod  into  the  mixture,  and  hold  it  near  the 
mouth  of  the  flask  which  is  giving  off  ammonia.  Dense  white 
fumes  of  sal  ammoniac  will  appear  around  the  rod. 

Gaseous  ammonia  becomes  liquid  at  a  cold  of  —  40°  C., 
and  by  a  pressure  of  about  7  atmospheres  at  15°.  It  may 
even  be  frozen  at  -  75°  C.  into  a  transparent  solid. 

Exp.  112. — Slip  a  piece  of  freshly-burned  charcoal  under  the 
edge  of  a  long  tube  previously  filled  with  dry  ammonia  gas,  and 
standing  over  mercury.  The  charcoal  will  quickly  absorb  the 
ammonia ;  if  pure,  the  whole  of  the  gas  will  disappear,  and  the 
mercury  will  fill  the  tube. 

Charcoal  has  this  power  of  absorbing  all  gases  to  a  greater 
or  less  extent ;  but  such  gases  as  are  freely  soluble  in  water 

\  more  easily  absorbed  by  charcoal  than  those  which  are 
ringly  soluble.  One  c.  c.  of  boxwood  charcoal  will  take  up 
fully  90  c.  c.  of  ammonia;  so  that  the  gas  is  subjected  to  a 
much  greater  degree  of  condensation  by  this  absorptive 
action  than  would  be  necessary  to  liquefy  it  by  pressure. 

A  solution  of  ammonia  is  in  constant  use  in  the  laboratory. 
It  may  easily  be  prepared  as  follows  : — 

Exp.  113. — Mix  from  30  to  50  grams  of  powdered  sal  ammo- 
niac with  an  equal  weight  of  slaked  lime,  and  place  the  mixture 
in  a  flask ;  then  add  30  or  40  c.  c.  of  water,  and  let  the  flask  be 
fitted  with  a  good  cork  and  bent  tube,  as  shown  in  Fig.  57. 
Next,  by  means  of  a  piece  of  vulcanised  tubing,  connect  the  bent 


Solution  of  Ammonia. 

tube  of  the  flask  with  a  three-necked  bottle  containing  water,  or 
with  a  wide-mouthed  bottle  fitted  with  a  cork  and  three  tubes, 
two  of  which  are  bent  at  right  angles.  Neither  of  these  bent 
tubes  must  dip  into  the  water.  The  second  bent  tube  may  pass 

Fig-  57- 


into  another  three-necked  bottle  containing  water,  the  first  bent 
tube  of  which 'passes  below  it,  and  the  second  bent  tube  into  a 
bottle  also  containing  water,  for  the  purpose  of  condensing  any 
of  the  gas  which  may  escape  from  the  first  two  vessels. 

A  bottle  of  this  kind  is  known  as  a  Woulfts  bottle]  and 
the  middle  tube,  open  at  both  ends  and  dipping  into  the 
liquid,  is  intended  to  admit  air,  if  the  gas  is  absorbed  by  the 
water  faster  than  it  is  supplied ;  at  the  same  time,  none  of  the 
gas  can  escape  through  it  into  the  atmosphere.  By  this 
contrivance  air  can  enter  the  partial  vacuum,  and  the  water 
in  the  outermost  bottle  is  prevented  from  being  driven  back 
by  atmospheric  pressure. 

The  solution  of  ammonia  is  lighter  than  water,  the  specific 
gravity  of  the  solution  diminishing  as  the  quantity  of  gas 
contained  in  it  increases.  The  water  also  increases  in  bulk 
as  it  dissolves  the  ammonia;  and  when  saturated  at  15°,  it 
contains  more  than  a  third  of  its  weight  of  the  alkali.  It  has 
the  intensely  pungent  odour  of  ammonia,  and,  when  gently 
heated,  gives  off  the  gas  in  large  quantity. 


Analysis  of  Ammonia  Gas. 


119 


Exp.  114. — Boil  a  little  of  a  strong  solution  of  ammonia  in  a 
flask  provided  with  a  cork  and  tube,  bent  as  shown  in  Fig.  58 : 
the  gas  will  come  off  freely.  Fig 

Apply  a  light  to  the  issuing 
gas  :  it  will  not  burn  readily, 
but  a  pale  greenish  flame 
will  play  over  the  top  of  the 
light.  Place  the  tube  from 
which  the  gas  is  escaping  in 
a  bottle  of  oxygen,  and  then 
apply  a  light  :  it  will  now 
burn  with  a  green  flame. 

Ammonia  consists  of  one 
measure  of  nitrogen  and  three  measures  of  hydrogen,  which 
become  condensed  into  the  space  of  two  measures  by  the 
act  of  combining — 


Ammonia  may  be  separated  into  its  two  constituent  gases 
by  passing  a  series  of  electric  sparks  through  a  quantity  of 
gaseous  ammonia  confined  in  a  tube  over  mercury.  By 
degrees  the  volume  of  the  gas  becomes  doubled ;  and  on 
then  causing  a  little  water  to  pass  up  into  the  tube  by  means 
of  a  bent  pipette  (Fig.  8),  the  gas  will  be  found  to  be  no 
longer  soluble  in  water ;  and  on  applying  a  lighted  match, 
the  hydrogen  in  the  mixture  will  take  fire.  The  quantity  of 
hydrogen  may  be  ascertained  by  introducing  (say)  8  measures 
of  the  gas  obtained  by  the  action  of  the  electric  sparks  upon 
ammonia  into  a  eudiometer,  and  then  adding  4  measures 
of  oxygen.  On  firing  the  mixture  by  the  electric  spark,  the 
12  measures  of  gas  will  become  reduced  to  3  ;  9  measures 
of  a  mixture  of  oxygen  and  hydrogen  in  the  proportions  to 
form  water  will  have  disappeared — in  other  words,  6  mea- 
sures of  hydrogen  will  have  combined  with  3  of  oxygen,  and 
become  condensed  as  water.  Consequently,  8  measures  of 
the  mixed  gas  from  the  ammonia  must  have  consisted  of  6 
measures  of  hydrogen  and  the  2  of  nitrogen  which  are  left. 


120 


CHAPTER  VI. 

SEA   SALT — HYDROCHLORIC  ACID. 

i.  CHLORINE.     2.  BROMINE.     3.  IODINE.    4.  FLUORINE. 

(24)  The  four  elementary  bodies,  chlorine,  bromine,  iodine, 
and  fluorine,  constitute  a  remarkable  group  of  closely  related 
substances.  Characterised  by  high  chemical  activity,  and 
by  the  power  of  forming  with  the  metals  compounds  ana- 
logous to  sea  salt,  they  have  hence  been  called  halogens,  or 
salt  producers,  from  a\c,  sea  salt. 

i.  CHLORINE:  Symb.  Cl;  Atomic  Wt.  35-5;  Mol.  Wt.  71; 
Atomic  Vol.  [];  Sp.  Gr.  2-435;  Rel-  Wt.  35-5;  Mol. 
Vol.  m  (Cla). 

Common  table  salt,  or  sodic  chloride  (NaCl),  is  the  most 
abundant  compound  of  chlorine.  It  is  from  this  substance 
almost  exclusively  that  chlorine  is  obtained ;  it  is  never 
found  uncombined  in  nature. 

Exp.  115.— Mix  32  grams  of  finely  powdered  manganese  di- 
oxide with  an  equal  weight  of  common  salt.  Introduce  them 
into  a  flask  provided  with  a  cork  and  bent  tube,  and  pour  upon 
the  mixture  84  c.  c.  of  oil  of  vitriol  previously  diluted  with 
60  c.  c.  of  water  and  allowed  to  cool.  On  heating  the  mixture 
gently,  chlorine  comes  off  as  a  dense  greenish-yellow  suffocating 
gas,  and  may  be  collected  in  dry  bottles  by  downward  displace- 
ment.* 

The  chemical  reactions  may  be  thus  shown : 

Manganese         Sodic  Sulphuric         Manganese        Hydric  Sodic        w  chlorine 

Dioxide        Chloride  Acid  Sulphate  Sulphate 

MnOa  +  2NaCl  +  3HaSO4  =  MnSO4  +2NaHSO4  +  2HZO  +  Cl, 

Owing  to  the  yellow  colour  of  the  gas,  it  can  easily  be  seen 
when  the  bottle  is  full.  Each  bottle,  as  it  becomes  filled 

*  The  experiment  should  be  made  either  in  an  outhouse  or  under  a 
chimney  where  there  is  a  strong  draught  to  carry  off  the  irritating 
vapours. 


Solution  of  Chlorine.  1 2 1 

with  the  gas,  should  be  closed  with  a  ground  stopper,  the 
side  of  which  should  be  greased.  If  the  gas  is  collected 
over  water,  much  is  wasted,  owing  to  its  solubility  in  this 
liquid.  Chlorine  cannot  be  collected  over  mercury,  as 
it  immediately  begins  to  combine  chemically  with  the  metal. 
Another  process  for  obtaining  chlorine  is  this  : — 
Exp.  1 1 6. — Place  in  a  flask  50  grams  of  powdered  manganese 
dioxide,  and  pour  upon  it  250  c.  c.  of  common  hydrochloric 
acid  previously  diluted  with  one-third  of  its  bulk  of  water  : 
chlorine  comes  off  freely,  on  heating  the  mixture. 

In  this  case  the  hydrogen  of  the  acid  is  wholly  converted 
into  water  by  the  oxygen  of  the  manganese  oxide ;  half  the 
chlorine  unites  with  the  manganese,  while  the  other  half 
comes  off  as  gas — 

MnO2  +  4HC1     =     MnCl2  +   2H2O  +  C12. 

Cold  water  dissolves  about  twice  its  bulk  of  chlorine. 

Exp.  117. — Remove  the  stopper  from  a  bottle  of  chlorine  gas, 
close  the  mouth  with  a  glass  plate,  plunge  the  mouth  of  the 
bottle  into  water,  and  remove  the  plate  :  a  little  water  will 
enter.  Close  the  bottle  with  the  plate,  and  shake  the  gas  and 
the  water  together.  Again  open  it  under  water  :  more  water  will 
enter ;  and  by  repeating  the  agitation  and  other  operations  again 
two  or  three  times,  a  solution  of  the  gas  in  water  will  be  obtained. 

The  solution  of  chlorine  must  be  kept  in  the  dark.  If 
exposed  to  a  strong  light,  water  is  decomposed  and  oxygen 
is  set  free.  The  hydrogen  of  the  decomposed  water  combines 
with  chlorine  to  form  hydrochloric  acid,  which  dissolves  in 
the  liquid,  and  this  will  redden  litmus,  and  not  bleach  it 
The  reaction  may  be  thus  represented  : 

2C12+   2H2O     =     4HC1  +  O2. 

Exp.  1 1 8. — Fill  a  litre  bottle  with  a  strong  solution  of  chlo- 
rine. Fit  a  sound  cork  to  the  neck  ;  pass  through  the  cork  a  quill 
tube  open  at  both  ends,  and  bent  twice  at  right  angles,  so  that 
the  tube  shall  reach  nearly  to  the  bottom  of  the  bottle.  Place 
it  in  direct  sunshine  :  gas  will  rise  into  the  upper  part  of  the 
bottle,  and  will  displace  the  solution,  which  must  be  allowed 


122  Properties  of  Chlorine. 

to  flow  over  into  a  vessel  placed  for  its  reception.  If  the  cork 
be  withdrawn  when  sufficient  gas  has  been  formed,  and  a  lighted 
match  be  introduced,  it  will  burn  briskly  in  the  liberated  oxygen. 

This  power  of  decomposing  water  and  of  setting  oxygen 
free  often  renders  chlorine  an  indirect  but  powerful  means  of 
forwarding  oxidation. 

The  solution  of  chlorine  has  the  smell  and  taste  of  the 
gas.  When  cooled  down  to  near  the  freezing  point  of  water, 
crystals  of  chlorine  hydrate  are  formed.  If  these  crystals  are 
put  into  a  strong  tube,  so  as  nearly  to  fill  it,  and  the  tube 
be  carefully  sealed,  the  crystals  will  melt  when  the  tempera- 
ture rises,  and  yellow  oily-looking  drops  of  liquid  chlorine 
will  separate,  and  subside  through  the  water.  They  exert 
at  15°  C.  a  pressure  equal  to  about  4  atmospheres. 

Chlorine  is  not  inflammable. 

Exp.  119. — Plunge  a  lighted  taper  into  the  gas  :  it  burns 
feebly,  with  a  red  smoky  flame. 

Chlorine  combines  at  once  with  many  elementary  sub- 
stances with  great  energy. 

Exp.  1 20. — Place  a  piece  of  dry  phosphorus  in  a  copper  de- 
flagrating spoon  ;  introduce  it  into  a  bottle  of  chlorine  gas  :  the 
phosphorus  takes  fire,  and  burns  with  a  pale  greenish  flame,  while 
suffocating  fumes  of  phosphoric  chloride  (PC15)  are  formed. 

Exp.  121. — Dip  a  strip  of  blotting-paper  into  oil  of  tur- 
pentine ;  plunge  it  into  a  jar  of  chlorine  gas  :  it  immediately 
bursts  into  flame,  whilst  a  dense  black  smoke  is  given  oif. 

In  this  case  the  chlorine  unites  with  the  hydrogen  of  the 
oil  of  turpentine,  and  the  carbon  is  separated. 

Exp.  122. — Powder  some  metallic  antimony  finely  in  a 
mortar,  and  sprinkle  a  little  of  it  into  a  jar  of  chlorine  :  it  takes 
fire  as  it  falls,  giving  out  fumes  of  antimonic  chloride  (SbCl5), 
which  are  very  irritating. 

Copper  leaf,  powdered  bismuth,  and  many  other  metals, 
when  in  a  sufficiently  finely  divided  state,  take  fire  when 
introduced  into  chlorine,  forming  chlorides  by  their  union 
with  the  gas.  In  all  cases  where  chlorine  combines  with 


Hydrogen  and  Chlorine.  123 

another  elementary  body,  the  new  compound  is  termed  a 
chloride. 

This  energetic  action  of  chlorine  renders  it  of  great  value 
as  a  disinfectant,  for  it  immediately  decomposes  all  animal 
effluvia  with  which  it  comes  into  contact,  and  converts  them 
into  new  and  harmless  substances. 

Another  very  important  property  of  chlorine  is  its  bleach- 
ing power.  Many  vegetable  and  animal  colours  are  attacked, 
when  moist,  by  chlorine,  which  removes  a  portion  of  their 
hydrogen,  while  a  corresponding  quantity  of  chlorine  takes 
its  place,  often  forming  a  substance  which  has  little  or  no 
colour.  In  other  cases  the  chlorine  acts  by  removing  hydro- 
gen from  water,  setting  oxygen  free,  and  this,  at  the  moment 
of  its  liberation,  decomposes  the  colouring  material. 

Exp.  123. — Pour  a  little  boiling  water  upon  some  chips  of 
logwood,  so  as  to  obtain  a  deep  red  liquid  :  add  a  little  of  the 
solution  of  chlorine,  and  the  red  colour  will  be  discharged. 

Common  writing-ink,  infusions  of  cochineal,  of  brazil- 
wood, of  litmus,  and  of  many  other  colouring  matters,  will 
also  be  bleached  by  it  with  facility.  Chlorine  is  very  ex- 
tensively used  for  bleaching  purposes  in  the  manufacture  of 
cotton  goods  and  of  paper,  as  well  as  in  calico  printing  and 
in  dyeing. 

(25)  HYDROCHLORIC  ACID  :  Symb.  HC1;  Atomic  Wt.  36-5; 
Atomic  and  MoL  Vol.  [~  ]];  Sp.  Gr.  1*2474;  Relative 
Wt.  18-25. 

Hydrogen  and  chlorine  have  a  very  powerful  attraction 
for  each  other.  If  equal  measures  of  the  two  gases  be  mixed 
together,  and  exposed  to  direct  sunlight,  or  other  strong 
light,  such  as  that  of  burning  magnesium,  they  combine 
instantly,  with  a  powerful  explosion ;  in  diffused  daylight  they 
gradually  unite,  but  the  mixture  may  be  preserved  unaltered 
if  kept  in  the  dark. 

Exp.  124.— Wrap  up  a  soda-water  bottle  in  a  towel;  fill  it 
with  water,  and  invert  it  in  the  pneumatic  trough.  Introduce  a 


124  Hydrochloric  Acid  Gas. 

glass  funnel  into  the  neck,  and,  having  filled  a  jar  of  100  c.  c. 
capacity  with  chlorine,  decant  the  gas  into  the  bottle.  Fill  the 
same  jar  with  hydrogen,  and  decant  that  into  the  same  bottle ; 
withdraw  the  funnel,  close  the  neck  with  the  palm  of  the  hand, 
lift  the  bottle  out  of  the  water-bath,  give  it  a  shake  to  mix  the 
gases,  and  apply  a  lighted  match.  A  sharp  explosion  imme- 
diately follows,  and  gaseous  hydrochloric  acid  is  formed. 

Equal  measures  of  hydrogen  and  chlorine  unite  in  this 
way,  and  the  gas  produced  occupies  the  same  bulk  that  its 
components  did  when  separate — 

[H]  +  [c|]    =    [Hjcih 

but  owing  to  the  action  of  chlorine  on  mercury,  and  its 
solubility  in  water,  it  is  not  easy  to  make  this  experiment 
with  accuracy. 

Hydrochloric  acid  gas  is  transparent  and  colourless;  it 
has  a  pungent  irritating  smell,  and  an  intensely  acid  taste ; 
it  also  makes  the  eyes  smart.  This  acid  is  not  inflammable, 
and  it  will  not  allow  a  candle  to  burn  in  it  It  is  also 
injurious  to  vegetation.  It  is  heavier  than  air,  and  is  very 
soluble  in  water,  producing  a  powerfully  acid  solution.  By 
a  very  strong  pressure,  the  gas  may  be  reduced  to  a  liquid, 
which  has  never  been  frozen. 

Exp.  125. — Melt  200  or  300  grams  of  common  salt  in  a  clay 
crucible  at  a  good  red  heat,  and  pour  out  the  salt  when  melted 
upon  a  dry  stone  slab,  or  into  a  clean  iron  shovel.  When  cold, 
break  up  the  mass  into  pieces  of  the  size  of  a  pea,  and  preserve 
them  in  a  dry  bottle.  Introduce  50  grams  of  the  chloride  *  into  a 
flask  provided  with  a  cork  and  bent  tube,  having  poured  over  it 
about  twice  its  weight  of  oil  of  vitriol.  Hydrochloric  acid  gas 
comes  off,  even  in  the  cold,  but  it  is  extracted  still  more 
abundantly  when  heated.  Collect  the  gas  in  diy  bottles  by 
downward  displacement.  It  may  easily  be  ascertained  when 
the  bottle  is  full,  as  a  lighted  taper  will  be  extinguished  if  in- 
troduced only  into  its  neck. 

*  Other  chlorides — such  as  chloride  of  potassium,  ammonium,  or 
calcium — might  be  used ;  but  common  salt,  as  the  cheapest,  is  always 
preferred  for  preparing  hydrochloric  acid. 


Analysis  of  Hydrochloric  Acid. 


12$ 


This  gas  emits  copious  whitish  fumes  as  it  escapes, into 
the  air,  owing  to  its  combining  with  the  moisture  of  the 
atmosphere,  and  condensing  it  into  the  form  of  liquid 
globules,  which  again  slowly  evaporate.  The  reaction  which 
accompanies  its  formation  may  be  thus  represented  : 
NaCl  +  H2SO4  =  HC1  +  NaHSO4. 

Exp.  126. — Fill  a  flask  with  the  gas  by  displacement,  close 
the  neck  with  the  thumb,  and  immerse  it  in  a  basin  containing 
infusion  of  litmus  ;  on  removing  the  thumb,  the  blue  liquid  will 
rush  into  the  flask,  and  will  become  red. 

The  presence  of  hydrogen  and  chlorine  in  the  acid  gas 
may  be  proved  analytically  as  follows  : — 

Exp.  127. — Heat  two  or  three  globules  of  sodium  of  the  size 
of  a  pea  in  a  copper  spoon  in  the  flame  of  a  spirit  lamp  till  they 
begin  to  burn ;  then  jrjgt  ^ 

plunge  them  into  a  jar 
of  hydrochloric  acid 
gas.  The  sodium  will 
take  fire  and  burn. 

In  this  experiment 
the  hydrochloric  acid 
is  decomposed,  the 
sodium  uniting  with 
the  chlorine  to  form 
common  salt,  while 
the  hydrogen  is  set 
free. 

Hydrochloric  acid 
contains  half  its  bulk 
of  hydrogen,  as  may 
be  shown  by  an 
exact  analysis  of  the 
gas  by  means  of  a  so- 
lution of  sodium  in  mercury,  which  may  be  effected  in  the 
following  manner: — Fill  a  bent  tube  (Fig.  59)  with  mer- 
cury, slip  a  piece  of  flexible  tube  over  the  end  of  a  quill  tube 


1 26  Solution  of  Hydrochloric  A  cid. 

connected  with  a  glass  flask  from  which  hydrochloric  acid  gas 
is  being  disengaged,  and,  having  passed  the  flexible  tube 
round  the  bend  into  the  closed  limb  of  the  U  tube,  allow 
hydrochloric  acid  to  pass  until  the  closed  limb  is  two-thirds 
full.  The  displaced  mercury  must  be  allowed  to  escape  at  the 
quill  tube,  on  which  the  screw-tap  is  relaxed ;  then  withdraw 
the  flask  and  tube,  and  close  the  screw-tap  on  the  U  tube. 
Pour  in  mercury  until  it  stands  at  the  same  level  in  both 
limbs.  Now  slip  a  small  elastic  ring  over  the  sealed  tube, 
so  as  to  mark  the  height  at  which  the  mercury  stands ;  fill 
up  the  open  limb  with  an  amalgam  of  sodium,  prepared  by 
dissolving  6  or  8  pieces  of  sodium  the  size  of  a  pea  in  30  c.  c. 
of  mercury.  Close  the  tube  with  a  good  cork.  Transfer  the 
gas  into  the  limb  containing  the  amalgam,  and  agitate  it 
briskly:  sodic  chloride  will  be  formed.  Retransfer  the  gas 
to  the  closed  limb,  allow  mercury  to  run  off  till  it  stands  at 
the  same  level  in  both  limbs  :  it  will  be  found  that  the  gas 
has  been  reduced  to  half  its  original  bulk,  and  that  which  is 
left  is  hydrogen,  for  it  will  burn  on  the  approach  of  a  light. 

Exp.  128. — Fill  a  dry  bottle  with  hydrochloric  acid  gas,  and 
close  the  mouth  with  a  glass  plate.  Withdraw  the  stopper  from 
a  bottle  of  ammoniacal  gas  of  the  same  size  ;  invert  the  jar  of 
hydrochloric  acid  over  the  one  containing  the  ammonia,  and 
remove  the  glass  plate.  The  two  invisible  gases  will  suddenly 
combine,  a  dense  white  cloud  will  be  formed,  and  a  solid  salt 
(sal  ammoniac,  or  ammonium  chloride)  will  be  produced. 

Equal  bulks  of  the  two  gases  unite  and  condense  each 
other,  HC1  +  H3N  becoming  H4NC1.  The  group  H4N  has 
never  been  obtained  in  a  separate  form ;  but  many  chemists 
regard  it  as  a  compound  metal,  called  ammonium,  which  com- 
bines with  chlorine,  and  completely  neutralises  its  activity, 
just  as  sodium  does  in  common  salt,  NaCl  resembling 
(H4N)C1  in  many  important  points. 

A  solution  of  hydrochloric  acid  in  water  forms  an  im- 
portant and  powerful  chemical  agent.  It  is  frequently 
spoken  of  as  muriatic -acid,  from  the  word  muria,  brine.  The 


Hydrochloric  A  cid.  127 

common  commercial  acid  has  often  a  yellow  colour,  owing 
to  the  presence  of  a  little  iron.  It  is  a  fuming  liquid,  of 
sp.  gr.  about  1*17,  and  contains  about  a  third  of  its  weight 
of  the  gas.  A  solution  of  hydrochloric  acid  may  readily  be 
prepared  by  connecting  a  flask  charged  with  a  mixture  of 
fused  salt  and  oil  of  vitriol  with  an  apparatus  similar  to  that 
employed  for  obtaining  a  solution  of  ammonia  (Fig.  5  7) .  This 
acid  dissolves  those  metals  which  decompose  steam  when 
passed  over  them  at  a  red  heat,  such  as  zinc,  iron,  nickel,  and 
tin,  with  escape  of  hydrogen,  while  chlorides  of  the  metals  are 

formed : 

Zn  +   2HC1     =     ZnCl2   +   H2. 

Exp.  129. — Dilute  a  little  hydrochloric  acid  with  6  or  8  times 
its  bulk  of  water,  and  add  caustic  soda  cautiously,  until  the 
liquid  is  exactly  neutral,  and  neither  reddens  blue  litmus 
nor  restores  the  blue  to  red  litmus  paper.  Pour  the  liquid  into 
a  basin,  and  evaporate  it  slowly  :  crystals  of  common  salt  will 
be  deposited  in  cubes. 

In  this  case  the  whole  of  the  hydrogen  of  the  acid,  in 
combination  with  oxygen  derived  from  the  soda,  will  pass 
off  as  water,  the  change  being  as  follows — 

HC1  +  NaHO     =     NaCl  +  H2O. 

Exp.  130. — Pass  a  piece  of  quicklime  into  a  tube  filled  with 
hydrochloric  acid  gas  standing  over  mercury:  the  gas  will  be 
quickly  absorbed. 

The  change  is  the  following  : — . 

CaO  -f   2HC1     =     CaCl2  +  H2O, 

calcic  chloride  and  water  being  formed. 

Most  of  the  chlorides  are  soluble  in  water ;  and  when  a 
solution  of  a  strong  base,  such  as  potash,  is  added  to  the 
solution  of  a  chloride  of  one  of  the  metals  which  forms  an 
insoluble  oxide,  the  oxide,  and  not  the  metal,  is  pre- 
cipitated. 

Exp.  131. — Add  a  solution  of  caustic  potash  to  a  diluted  solu- 
tion of  cupric  chloride. 


128  Hydrochloric  A  cid. 

In  this  case  hydrated  cupric  oxide  is  thrown  down,  of  a 
pale  blue  colour — 

CuCl2  +   2KHO    •=     2KC1  +  CuH202. 

If  a  more  complex  oxide  be  acted  on,  a  corresponding 
chloride  is  formed,  if  the  formation  of  such  a  compound  be 
possible.  For  instance,  ferric  oxide  may  be  dissolved  by 
hydrochloric  acid,  and  the  change  is  thus  shown — 
Fe2O3  +  6HC1  =  Fe2Cl6  +  sH2O. 
But  if  there  be  no  chloride  corresponding  to  the  oxide,  part 
of  the  chlorine  escapes,  while  a  chloride  of  simpler  com- 
position is  formed,  as  in  the  common  process  of  obtaining 
chlorine  gas,  by  acting  on  manganese  dioxide,  to  which  there 
is  no  corresponding  chloride,  MnO2  +  4-HC1  becoming 
MnCl2  +  2H2O  +  C12. 

Hydrochloric  acid  and  the  chlorides  are  easily  distin- 
guished when  present  in  solution  by  the  following  tests  : — 

E.rp.  132. — Dissolve  0*2  gram  of  sodic  chloride  in  100  c.  c. 
of  water,  and  divide  it  into  two.  portions,  (i)  To  one  of  these  add 
a  few  drops  of  a  solution  of  argentic  nitrate  :  an  abundant  white 
cloud  of  argentic  chloride  (AgCl)  will  be  formed.  Divide  this 
milky  liquid  into  two  portions.  To  one  of  them  add  a  few  drops 
of  nitric  acid  :  no  change  will  be  perceptible.  To  the  other  add 
a  few  drops  of  ammonia  solution  :  the  liquid  will  become  clear, 
since  ammonia  dissolves  argentic  chloride  readily.  (2)  To  another 
portion  of  the  sodic  chloride  solution  add  a  few  drops  of  a  solu- 
tion of  mercurous  nitrate  :  a  white  precipitate  of  calomel  will 
appear.  Divide  this  turbid  solution  into  two  portions.  Add  a 
few  drops  of  nitric  acid  to  one  :  no  change  will  occur.  To  the 
other  add  ammonia :  the  precipitate  will  become  black. 

Exp.  133. — Boil  hydrochloric  acid  in  a  test-tube  with  frag- 
ments of  gold  leaf:  they  will  not  be  dissolved.  Now  add  a 
drop  or  two  of  nitric  acid  :  a  yellow  solution  of  auric  chloride 
(AuCl3)  will  be  quickly  formed. 

Scraps  of  platinum  are  not  dissolved  by  hydrochloric 
acid,  but  they  enter  slowly  into  solution  if  nitric  acid  be 
added  and  the  mixture  be  warmed.  This  mixture  of  hydro- 
chloric with  nitric  acid  is  often  called  aqua  regia  (royal  water), 


Compounds  of  Chlorine  and  Oxygen.  1 29 

from  its  power  of  dissolving  gold,  which  was  regarded  by  the 
alchemists  as  the  king  of  metals.  This  mixture  of  acids  is 
often  useful  for  dissolving  ores  which  resist  either  acid  singly. 
It  owes  its  activity  to  the  chlorine  which  is  set  free.  In 
using  the  liquid,  it  should  be  only  gently  warmed,  because 
if  boiled  the  chlorine  is  quickly  expelled  to  waste.  Some 
oxy chlorides  of  nitrogen  are  formed  at  the  same  time,  and 
pass  off  in  red  vapours ;  but  the  chlorine  is  really  the  active 
substance — 

2HC1  +  HNO3     =     H2O  +  HNO2  +  C12. 
If  the  hydrochloric  acid  be  used  in  excess,  chlorides  only 
remain  in  the  liquid,  the  whole  of  the  nitric  acid  being  de- 
composed and  going  off  with  the  gases. 

(26)  Oxides  of  Chlorine.  —  Chlorine  does  not  combine 
directly  with  oxygen,  but  it  forms  with  it  three  gaseous  com- 
pounds, all  of  which  have  a  red  or  yellow  colour,  a  peculiar 
irritating  odour,  a  corrosive  action,  and  are  all  so  unstable 
that  they  are  easily  decomposed  by  heat,  and  explode  with 
violence.  These  gases  are : 

Hypochlorous  anhydride       .         .         .     ClaO 
Chlorous  anhydride      ....     ClaO3 

Chloric  oxide CIO, 

The  first  two,  when  acted  on  by  water,  furnish  aci4s ;  and, 
in  addition,  two  other  acids  containing  chlorine  and  oxygen 
are  known.  These  acids  form  a  regular  series,  in  which  the 
oxygen  increases  step  by  step  as  follows : 

Hypochlorous  acid       .        .  .     HC1O 

Chlorous  acid       ...  .     HClOa 

Chloric  acid HC1O3 

Perchloric  acid HC1O4 

All  these  acids  are  very  unstable,  and  they  are  seldom 
prepared.  Some  of  their  salts,  particularly  the  hypochlorites 
and  chlorates,  are  important. 

Some  of  these  salts  are  formed  by  acting  upon  a  strong 
base  with  chlorine ;  but  the  result  varies  according  to  the 
temperature  employed. 


130  Chlorine  A  cids. 

Exp.  1 34. — Cause  a  current  of  chlorine  gas  to  pass  slowly  into 
a  dilute  solution  of  potash  which  is  to  be  kept  cool. 

In  this  case  a  liquid  is  obtained  which  possesses  bleaching 
properties,  and  in  which  a  mixture  of  two  salts  (potassic 
chloride  and  potassic  hypochlorite)  is  formed — 

C12  +   2KHO     =     KC1  +  KC1O  +  H2O.* 

Exp.  135. — Repeat  the  experiment  on  a  stronger  solution  of 
potash  (i  of  potash  to  3  of  water)  which  is  to  be  heated. 

In  this  case  also  the  chlorine  will  be  absorbed,  but  potassic 
chlorate  and  potassic  chloride  will  now  be  formed,  and  no 
bleaching  liquor  will  be  obtained — 

3C12  +  6KHO     =     sKCl  +  KC103  +  3H2O. 

The  potassic  chlorate  is  sparingly  soluble ;  and  if  the  solu- 
tion be  evaporated  to  a  small  quantity,  and  then  allowed  to 
cool,  flat  tables  of  the  salt  will  crystallise  out.  If  the  solu- 
tion be  poured  off  from  these  crystals,  and  they  be  re- 
dissolved  in  a  small  quantity  of  boiling  water,  the  second 
crop  of  crystals  will  be  nearly  pure.  This  is  the  salt  usually 
employed  for  obtaining  oxygen  by  decomposing  it  at  a  high 
temperature.  {See  Appendix.) 

Exp.  136. — Dissolve  a  few  crystals  of  the  pure  chlorate  in 
water,  and  add  a  little  solution  of  argentic  nitrate. 

In  this  case  no  precipitate  is  formed,  because  argentic 
chlorate  is  soluble. 

Exp.  137. — Heat  some  of  the  crystals  in  a  test-tube  as  long 
as  they  give  off  oxygen.  When  cold,  dissolve  the  white  residue 
in  water. 

The  solution  will  now  precipitate  the  argentic  nitrate 
abundantly ;  the  chlorate  has  been  decomposed  into  oxygen 
and  potassic  chloride,  and  this  salt  immediately  forms  ar- 
gentic chloride  with  the  nitrate — 

2KC103     =     2KC1  +  302. 

*  Bleaching  powder,  or  chloride  of  lime,  is  a  similar  compound.  It 
is  manufactured  on  a  large  scale  by  passing  chlorine  gas  through  boxes 
containing  trays  of  slaked  lime. 


Chlorides  and  Chlorates.  131 

Chloric  acid  is  very  unstable,  and  is  rarely  prepared.  No 
attempt  must  be  made  to  obtain  it  by  distilling  potassic 
chlorate  with  sulphuric  acid,  in  imitation  of  the  process  for 
nitric  acid. 

Exp.  138. — Put  two  drops  of  oil  of  vitriol  in  a  test-tube ;  throw 
in  a  crystal  of  potassic  chlorate  of  about  the  size  of  a  split  pea, 
holding  the  mouth  of  the  tube  away  from  you,  and  warm  the 
mixture.  A  dense  brownish-yellow  gas,  of  peculiar  irritating 
odour,  will  come  off,  and  at  a  heat  below  that  of  boiling  water 
a  loud  cracking  sound  or  small  explosion  will  occur. 

The  sulphuric  acid  in  this  case  decomposes  the  chlorate, 
and  liberates  chloric  acid,  which  immediately  breaks  up  into 
chloric  oxide,  and  potassic  perchlorate,  while  the  chloric  oxide 
when  heated  is  in  turn  decomposed  with  explosion.  The 
following  equation  represents  the  change : — 

Potassic  Sulphuric  Chloric  Potassic         Hydric  Potassic     w  . 

Chlorate  Acid  Oxide          Perchlorate  Sulphate 

3KC1O5   +   2HaSO4   =   2C1O,   +   KC1O4   +   2KHSO4   +  HaO 

Exp.  139. — Put  two  or  three  crystals  of  potassic  chlorate  into 
a  wineglass,  and  pour  some  water  upon  them.  Add  a  piece  of 
phosphorus  of  the  size  of  a  split  pea.  Place  the  glass  upon  a 
soup  plate,  and  with  a  long-necked  funnel  reaching  to  the  bottom 
of  the  glass  pour  in  quietly  about  a  teaspoonful  of  oil  of  vitriol. 
As  soon  as  the  acid  reaches  the  bottom  a  crackling  noise  is 
heard,  and  flashes  of  a  green  light  are  produced,  owing  to  the 
burning  of  the  phosphorus  under  water  in  the  chloric  oxide  as 
it  is  formed. 

Exp.  140. — Melt  a  little  potassic  chlorate  in  a  test-tube,  and 
heat  it  moderately  as  long  as  it  gives  off  gas  freely.  If  the  ex- 
periment be  carefully  watched,  the  salt  will  be  seen  gradually  to 
become  pasty ;  when  this  occurs,  remove  the  tube  from  the 
lamp  and  set  it  to  cool.  Treat  what  is  left  first  with  cold  water, 
and  then  dissolve  the  sparingly  soluble  residue  in  boiling  water ; 
as  it  cools  a  new  salt,  the  potassic  perchlorate,  will  crystallise. 

The  chlorate  in  this  operation  loses  one-third  only  of  its 
oxygen.     When  heated,  it  becomes  separated  into  two  new 
salts,  potassic  chlorite  and  potassic  perchlorate — 
2KC1O3     =     KC1O2  +  KC1O4; 


132  Sources  of  Bromine. 

but  the  chlorite  is  decomposed,  as  fast  as  it  is  formed,  into 
oxygen  gas  and  potassic  chloride — 

KC102     =     KC1  +  02; 

and  the  chloride,  which  is  very  soluble,  is  easily  separated 
from  the  sparingly  soluble  potassic  perchlorate.  If  the  per- 
chlorate  be  heated  still  more  strongly,  it  in  turn  is  decom- 
posed into  oxygen  gas  and  potassic  chloride — 

KC1O4     =     KC1  +   2O2. 

(27)  2.  BROMINE:  Symb.  Br;  Atom.  Wt.  80 ;  Atom. 
Vol.  Q;  Mol  Wt.  (Br2)  160;  Mol.  Vol.  fTH  ;  Rel.  Wt. 
80;  Sp.  gr.  of  vapour,  5-54 ;  of  liquid  at  o°  C.  3*187 ;  Boils 
at  63°  C. ;  Freezes  at  —12-5°. 

Bromine  is  the  only  element  except  mercury  which  is 
liquid  at  ordinary  temperatures.  It  is  of  a  deep  red  colour, 
and  gives  off  abundant  dark  red  vapours,  which  have  a  very 
irritating  effect  upon  the  eyes  and  the  back  of  the  throat, 
with  a  peculiar  disagreeable  odour,  whence  its  name  is 
derived.  It  is  about  three  times  as  heavy  as  water,  and  is 
but  sparingly  soluble  in  it,  but  freely  so  in  alcohol  and 
ether.  Its  chemical  properties  are  similar  to  those  of 
chlorine,  but  less  active.  It  forms  a  gaseous  compound  with 
hydrogen,  the  hydrobromic  acid  (HBr  =  81 ;  Sp.  Gr.  2*731 ; 
Rel.  Wt.  42-5),  which  fumes  in  air  and  is  extremely  soluble 
in  water ;  it  is  powerfully  acid,  and  much  resembles  hydro- 
chloric acid.  It  may  be  obtained  by  decomposing  potassic 
bromide  with  phosphoric  acid.  Bromine  also  forms  acids 
in  which  oxygen  is  present ;  but  only  two  of  them — the 
bromic  (HBrO3),  corresponding  to  the  chloric,  and  per- 
bromic  (HBrO4),  corresponding  to  the  perchloric — have 
been  examined  carefully. 

Bromine  is  contained  in  sea  water,  as  magnesic  bromide 
(MgBr2),  in  quantity  varying  from  4  to  14  mgrams.  per  litre. 

Sea  water  is  concentrated  in  large  quantities  for  the  sake 
of  its  common  salt  and  potassic  and  magnesic  salts ;  and 
when  these  have  been  separated  by  crystallisation,  the  mother 


Formation  of  Bromine.  133 

liquor,  or  bittern,  is  treated  for  the  bromine.  Many  strong 
brine  springs,  such  as  those  of  Kreuznach  and  Kissingen, 
also  contain  small  quantities  of  the  bromides.  The  bittern 
is  made  to  yield  its  bromine  by  transmitting  into  it  a  current 
of  chlorine  gas,  avoiding  an  excess  of  it.  All  the  bromides 
of  the  metals  are  decomposed  by  chlorine,  which  has  a  more 
powerful  attraction  for  the  metals  than  bromine  has.  The 
liquid  acquires  a  beautiful  golden  yellow  colour,  due  to  the 
liberated  bromine,  MgBr2  +  C12  becoming  MgCl2  +  Br2. 
This  yellow  liquid  is  then  mixed  with  ethex  and  shaken  up 
with  it.  The  ether  dissolves  the  bromine ;  and  if  the  mixture 
be  placed  in  a  glass  globe,  provided  with  a  stopper  at  top 
and  a  glass  stop-cock  at  bottom,  the  ether  rises  in  a  yellow 
layer  to  the  surface,  and  the  mother  liquor  is  easily  drawn 
off  from  below.  The  ethereal  solution  is  then  shaken  up  with 
a  solution  of  caustic  potash,  by  which  the  yellow  colour  is 
immediately  destroyed:  potassic  bromide  and  bromate  are 
formed,  and  become  dissolved  in  the  water,  while  the  ether 
rises  to  the  surface,  and  may  again  be  used  in  a  similar 
manner  with  fresh  portions  of  bittern.  The  action  of  potash 
upon  bromine  resembles  that  which  it  exerts  upon  chlorine, 
3Br2  +  6KHO  yielding  KBrO3  +  sKBr  +  jH.O.  When 
the  solution  of  potash  has  become  neutralised  by  the -action 
of  repeated  charges  of  bromine,  the  liquid  is  evaporated  to 
dryness,  mixed  with  a  little  charcoal,  and  gently  heated,  to 
remove  the  oxygen  from  the  bromate ;  after  which  the 
residue,  consisting  of  bromide  and  the  excess  of  charcoal,  is 
mixed  with  manganese  dioxide  and  sulphuric  acid  in  a  retort 
On  applying  heat,  red  vapours  of  bromine  pass  over — • 
2KBr+MnO2  +  3H2SO4=2KHSO4  +  MnSO4-f  2H2O-fBr2. 
The  reaction  resembles  that  by  which  chlorine  is  obtained. 

Exp.  141. — Dissolve  2  or  3  decigrams  of  potassic  bromide 
in  20  c.  c.  of  water.  Mix  the  solution  in  a  long  and  wide  test- 
tube,  with  5  c.  c.  of  solution  of  chlorine,  and  add  5  c.  c.  of  ether. 
Agitate  the  mixture  :  a  yellow  solution  of  bromine  in  ether  will 
rise  to  the  surface.  Decant  this  ethereal  solution  into  another 


134  Iodine. 

tube,  and  shake  it  with  an  equal  bulk  of  a  solution  of  caustic 
potash.  The  yellow  colour  will  disappear,  and  the  ether  will 
rise  to  the  top,  and  form  a  colourless  layer. 

Bromine  combines  directly  with  phosphorus,  and  with 
many  of  the  metals.  The  compound  formed  by  the  union 
of  bromine  with  any  other  element  is  called  a  bromide. 
Argentic  bromide  is  a  substance  of  importance  to  the 
photographer. 

Exp.  142. — Add  a  little  of  a  solution  of  argentic  nitrate  to  a 
weak  solution  of  potassic  bromide  :  a  white  precipitate  is  formed. 
Divide  the  liquid  with  the  precipitate  into  three  portions.  To  one 
of  them  add  a  little  nitric  acid,  to  another  a  few  drops  of  a  solution 
of  ammonia  :  no  solution  occurs  in  either  case.  To  the  third  add 
a  little  of  a  solution  of  sodic  hyposulphite  :  the  liquid  becomes 
clear,  a  double  hyposulphite  of  silver  and  sodium  being  formed. 

The  bromides  also  form  a  white  precipitate  of  mercurous 
bromide  (HgBr)  with  a  solution  of  mercurous  nitrate  ;  and  a 
white  precipitate  with  lead  nitrate,  consisting  of  lead  bromide 
(PbBr2).  Chlorine  water  decomposes  both,  setting  bromine 
free,  and  forming  a  chloride  of  mercury  or  of  lead. 

(28)  3.  IODINE:  Symb.  I;  Atomic  Wt.  127;  Atomic  vol. 
of  vapour  Q  ;  Mol.  Vol.  [_|J  (I2) ;  Rel.  Wt.  127;  Sp.  gr. 
of  vapour,  8716;  of  solid,  4*947;  Melting  Pt.  107°  C. ; 
Boiling  Pt.  175°  C. 

Iodine  is  a  solid,  which  crystallises  in  bluish-black  scales, 
resembling  plumbago  in  lustre.  It  is  volatile  at  ordinary 
temperatures,  and  emits  a  feeble  smell,  resembling  that  of 
chlorine,  and  sublimes*  slowly  in  the  bottles  in  which  it  is 
kept,  and  is  deposited  in  crystals  on  the  sides.  When  heated 
to  a  little  beyond  100°  C.  it  melts,  and  at  a  higher  tem- 
perature gives  off  dense  vapours,  of  a  rich  violet  hue,  whence 
it  derives  its  name. 

*  A  body  which  rises  in  vapour  and  condenses  in  the  solid  form  is 
said  to  sublime,  in  opposition  to  on«  which  condenses  in  the  liquid 
form,  when  it  is  said  to  distil. 


Tests  for  Iodine.  135 

Exp.  143. — Place  about  0-2  gram  of  iodine  in  a  flask ;  warm  it 
over  a  lamp.  The  iodine  will  melt  to  a  brown  liquid  ;  and  if  the 
flask  be  heated  gradually  and  uniformly,  beautiful  violet  vapours 
will  fill  it.  When  allowed  to  cool,  its  interior  will  be  coated 
over  with  small  crystals  of  sublimed  iodine. 

Iodine  stains  the  skin  and  most  organised  substances 
brown,  and  gradually  corrodes  them.  Water  dissolves  it  but 
sparingly,  alcohol  and  ether  freely;  solutions  of  the  iodides 
in  water  also  dissolve  it. 

Exp.  144. — Take  four  test-tubes,  and  place  about  a  decigram 
of  iodine  in  each.  Pour  into  the  first  2  c.  c.  of  water,  into 
the  second  the  same  quantity  of  alcohol,  into  the  third  the  same 
quantity  of  ether,  to  the  fourth  add  0*2  gram  of  potassic  iodide, 
and  then  a  little  water.  A  pale-yellow  liquid  will  be  formed  in 
the  first  tube,  and  scarcely  any  iodine  will  be  dissolved,  whilst  the 
iodine  will  be  dissolved  in  each  of  the  other  tubes,  and  will  form 
a  deep-brown  solution.  Mix  the  solution  in  alcohol  with  twice 
its  bulk  of  water  :  most  of  the  iodine  will  separate  in  scales,  as 
it  is  not  soluble  in  water,  and  the  water  immediately  separates 
the  alcohol  from  the  iodine.  Mix  the  solution  in  the  fourth  tube 
with  water  :  no  precipitation  will  occur,  because  the  potassic 
iodide  retains  the  iodide  dissolved. 

Exp.  145. — Place  about  0*3  gram  of  iodine  in  a  test-tube 
with  a  few  drops  of  water,  and  add  about  cri  gram  of  iron 
filings  :  a  green  solution  of  ferrous  iodide  will  be  formed. 

Exp.  146. — Let  zinc  filings  be  substituted  for  iron,  and  a 
colourless  solution  of  zinc  iodide  will  be  obtained. 

When  an  element  combines  with  iodine,  the  compound  is 
known  as  an  iodide. 

All  the  iodides  of  the  metals  are  readily  decomposed  by 
chlorine,  and  even  by  bromine,  while  the  iodine  is  set  free. 
This  is  taken  advantage  of  in  testing  for  iodine.  The  most 
delicate  test  for  free  iodine  is  the  intense  blue  colour  which 
it  yields  with  cold  starch  paste. 

Exp.  147. — Mix  i  gram  of  white  starch  with  10  grams  of 
water,  and  pour  it  slowly  into  40  or  50  grams  of  boiling  water ; 
boil  for  a  minute,  and  allow  it  to  cool.  Mix  a  little  of  this 
mucilage  with  water,  and  add  one  or  two  drops  of  any  of  the 


136  Source  of  Iodine. 

solutions  of  iodine  prepared  as  above  directed  :  the  intense  blue 
iodide  of  starch  is  immediately  formed. 

Exp.  148. — Mix  one  or  two  drops  of  a  solution  of  potassic 
iodide  with  a  little  of  the  diluted  starch  mucilage  :  no  change 
of  colour  will  occur.  Add  a  single  drop  of  chlorine  water  to  the 
mixture  :  an  immediate  coloration  will  occur,  owing  to  the  com- 
bination of  the  chlorine  with  the  potassium,  while  iodine  is  set 
free,  and  acts  upon  the  starch.  Add  a  little  more  chlorine 
water  :  the  colour  disappears,  owing  to  the  formation  of  chlorine 
iodide,  which  is  without  action  on  starch. 

A  solution  of  bleaching  powder  may  be  used  instead  of 
chlorine  water,  or,  still  better,  a  solution  of  potassic 
nitrite,  to  which  a  drop  or  two  of  acetic  acid  has  been 
added.  An  excess  of  nitrite  does  not  interfere  with  the  blue 
colour. 

Exp.  149. — Heat  the  blue  solution  of  starch  iodide  to  boiling  : 
the  colour  fades,  and  often  quite  disappears.  Cool  the  solution, 
and  the  blue  colour  returns. 

The  cause  of  this  change  of  colour  is  not  known . 

Other  tests  for  the  iodides,  though  of  less  delicacy,  are  the 
following  :  A  solution  of  lead  salt,  when  mixed  with  a  soluble 
iodide,  gives  beautiful  silky  yellow  scales  of  lead  iodide 
(PbI2).  A  silver  salt,  such  as  argentic  nitrate,  gives  a  pale 
buff- coloured  argentic  iodide  (Agl),  nearly  insoluble  in  am- 
monia. Mercuric  chloride  gives  a  yellow  precipitate  of 
mercuric  iodide  (HgI2),  quickly  passing  into  scarlet. 

Exp.  150. — Divide  the  last  named  solution  with  its  precipitate 
into  two  portions.  To  one  portion  add  a  little  more  of  the  mer- 
curial solution  :  the  precipitate  will  be  redissolved.  To  the  other 
portion  add  an  excess  of  potassic  iodide  :  this  also  will  re- 
dissolve  the  precipitate. 

Hence  it  will  be  seen  that  an  excess  of  either  salt  must  be 
avoided  when  testing  for  iodides  or  for  mercury. 

Iodine  is  contained  in  minute  proportion  in  sea  water, 
from  which  it  is  extracted  by  the  sea-weeds  during  their 
growth,  and  stored  in  their  tissues.  In  order  to  obtain  the 
iodine,  the  weeds  are  first  dried  in  the  sun,  and  then  burned, 


Hydriodic  A  cid.  137 

at  a  low  temperature,  in  shallow  pits  on  the  shore ;  the  ashes 
forming  what  is  called  kelp.  The  iodine  is  present  in  this 
ash  as  sodic  iodide.  The  soluble  matters  are  washed  out  of 
the  ash,  and  the  liquor  is  evaporated,  to  allow  most  of  the 
salts  of  potassium  and  sodium  to  crystallise  out.  Sulphuric 
acid  is  then  added  to  the  mother  liquor;  and  after  the  effer- 
vescence due  to  the  escape  of  carbonic  anhydride  and  gaseous 
compounds  of  sulphur  is  over,  the  acid  liquor  is  run  off  into 
stills,  mixed  with  powdered  manganese  dioxide,  and  distilled 
at  a  gentle  heat — 

2NaI  +  MnO,  +  3H3SO4  =  2NaHSO4  +  MnSO4  +  2H,O+  Ia. 
The  decomposition  which  occurs  resembles  that  which 
attends  the  liberation  of  chlorine  or  of  bromine,  as  already 
described.  Violet  vapours  of  iodine  come  off,  and  are 
condensed  in  a  series  of  globular  receivers.  The  crude 
iodine  thus  obtained  is  purified  by  a  second  sublimation. 

HYDRIODIC  ACID  :  Symb.  HI;  Atom,  and MoL  Wt.  128; 
Mol.  Vol.  m ;  Sp.  Gr.  4-443 ;  R^  Wt.  64. 

Exp.  151. — Dry  a  piece  of  phosphorus  of  the  size  of  a  split 
pea,  and  place  it  on  a  saucer.  Then  let  a  few  crystals  of  iodine 
fall  upon  it.  In  a  few  moments  the  two  bodies  will  unite,  and 
so  much  heat  will  be  given  out  that  the  phosphorus  will  take  fire. 

In  this  experiment  one  portion  of  phosphorus  burns  in  the 
air,  while  another  portion  unites  with  the  iodine  to  form 
phosphorous  iodide  (PI3). 

Exp.  152. — Place  in  a  small  retort  2  grams  of  iodine,  i  c.  c. 
of  water,  and  then  add  o-i  gram  of  phosphorus: 

In  this  case  phosphorous  iodide  is  also  formed  as  before, 
but  it  is  now  decomposed  by  the  water,  and  phosphorous 
and  hydriodic  acids  are  formed — 

PI3  +  3H20  =  H2PH03  +  3HL 

On  heating  the  mixture  gently,  hydriodic  acid  gas  will 
escape,  and  may  be  collected  by  downward  displacement  in 
a  wide  test-tube. 


138  Hydrofluoric  A  cid. 

Hydriodic  acid  gas  extinguishes  a  light,  and  does  not 
itself  burn ;  it  is  more  than  four  times  as  heavy  as  atmospheric 
air;  it  is  colourless,  but  fumes  strongly  when  it  escapes,  owing 
to  its  condensing  the  moisture  present  in  the  air.  It  is  very 
soluble  in  water,  with  which  it  forms  an  intensely  acid 
liquid.  Chlorine  immediately  decomposes  it,  and  sets  iodine 
at  liberty.  Its  solution  in  water,  if  exposed  to  the  air, 
gradually  absorbs  oxygen ;  the  hydrogen  unites  with  the  oxy- 
gen, and  the  liquid  becomes  brown  from  liberated  iodine — 
4HI  +  02  =  2H20  +  2la. 

Iodine  forms  a  white  oxide,  iodic  anhydride  (I2O5),  corre- 
sponding to  nitric  anhydride.  There  are  also  two  acids  of 
iodine  containing  oxygen,  viz.  the  iodic  (HIO3)  and  the 
periodic  (HIO4) ;  but  they  are  not  of  practical  importance. 

(29)  4.  FLUORINE:  Symb.  F;  Atom.  Wt.  19. 

Many  unsuccessful  attempts  have  been  made  to  obtain 
fluorine  in  an  isolated  state,  but  its  chemical  activity  is  so 
great  that  it  combines  with  the  metal  or  glass  with  which  it 
is  in  contact  at  the  moment  that  it  is  set  free ;  so  that  no 
satisfactory  knowledge  of  free  fluorine  has  yet  been  obtained. 
Its  compounds  with  other  elements  are  \ATO\&^  fluorides. 

The  most  important  and  abundant  natural  compound  of 
fluorine  is  calcic  fluoride  or  fluor  spar  (CaF2),  a  mineral 
which  is  insoluble  in  water,  colourless  when  pure,  but  more 
frequently  met  with  in  beautifully-veined  blue  or  green 
masses,  which,  when  crystallised,  occur  in  cubes,  or  some 
forms  derived  from  the  cube. 

Cryolite,  a  fluoride  of  aluminum  and  sodium  (3NaF,  A1F3), 
is  also  found  abundantly  in  Greenland. 

No  oxides  or  oxygen  acids  of  fluorine  are  known;  but 
when  combined  with  hydrogen,  it  furnishes  an  intensely 
corrosive  acid,  the  hydrofluoric  (HF),  which  immediately 
attacks  glass,  so  that  it  cannot  be  prepared  or  preserved  in 
glass  vessels.  Its  fumes  are  dangerously  irritating,  and 
great  care  must  be  taken  to  avoid  inhaling  them.  The  acid 


Its  Action  on  Glass.  139 

is  freely  soluble  in  water,  and  is  often  prepared  in  a  diluted 
form  for  etching  on  glass,  as,  for  instance,  in  engraving 
thermometer  scales,  and  for  similar  purposes.  This  diluted 
acid  may  be  preserved  in  silver  or  leaden  bottles,  or,  as  is 
more  usual,  in  vessels  made  of  gutta  percha. 

Exp.  153. — Powder  a  gram  of  fluor  spar  finely,  and  place  it 
in  a  small  shallow  leaden  cup,  6  or  8  centim.  in  diameter,  and 
pour  over  it  2  or  3  grams  of  oil  of  vitriol;  then  place  over  the 
leaden  cup  a  plate  of  glass  large  enough  to  cover  it,  prepared  in 
the  following  manner  : — Cover  one  side  of  the  glass  with  a  thin 
uniform  layer  of  beeswax,  which  may  be  done  by  warming  the 
glass  and  rubbing  it  over  with  the  wax.  When  the  glass  is  cold, 
trace  a  few  characters  with  the  point  of  a  knife  through  the  wax, 
so  as  to  expose  the  glass  beneath.  Place  the  glass  with  the 
waxed  surface  downwards  over  the  leaden  dish,  and  warm  it 
gently,  taking  care  not  to  melt  the  wax.  Vapours  of  hydrofluoric 
acid  will  be  given  off,  which  in  a  few  minutes  will  corrode  the 
glass  where  it  is  exposed,  but  will  not  attack  the  wax. 

The  acid  acts  on  the  fluor  spar  in  the  following  manner  : — 

CaF2  +  H2SO4  =  CaSO4  +  2HF. 
On  cleaning  off  the  beeswax  with  a  little  oil  of  turpentine, 
the  design  will  be  found  more  or  less  distinctly  etched  upon 
the  glass  plate.  A  very  small  quantity  of  fluorine  compound 
may  be  detected  in  a  mixture  by  proceeding  carefully  in  the 
same  manner.  In  the  enamel  of  the  teeth,  and  often  in 
fossil  bones,  fluorine  exists  in  quantity  sufficient  to  be  easily 
detected  in  this  way. 

The  hydrofluoric  acid  attacks  the  silica  of  the  glass,  fur- 
nishing water  and  gaseous  silicic  fluoride — 

SiO2  +  4HF    =    SiF4  +   2H2O. 

This  action  of  hydrofluoric  acid  renders  it  a  valuable  agent  in 
the  analysis  of  the  silicates  in  many  cases  where  the  ordinary 
acids  do  not  decompose  them.  Argentic  fluoride  is  soluble, 
so  that  the  fluorides  give  no  precipitate  with  argentic  nitrate. 
The  acid  unites  with  potassic  fluoride,  and  forms  a  crystalline 
compound  (KF,  HF),  from  which  the  anhydrous  hydro- 
fluoric acid  has  been  obtained.  (See  Appendix.) 


140  Hydrogen  and  the  Halogens. 

All  the  halogens  —  fluorine,  chlorine,  bromine,  and  iodine 
—  are  regarded  as  monads,  since  they  are  characterised  by 
forming  a  very  soluble  powerfully  acid  gas  when  united  with 
hydrogen,  such  as  the  hydrofluoric,  hydrochloric,  hydro- 
bromic,  and  hydriodic.  No  condensation  accompanies  the 
combination,  for  analysis  shows  that  in  each  case  the  acid 
contains  half  its  bulk  of  hydrogen,  the  hydrogen  being 
united  with  its  own  volume  of  the  halogen,  the  gaseous  acid 
occupying  the  same  bulk  as  its  component  gases  of  vapours 
did  in  their  separate  form. 

With  the  exception  of  fluorine,  each  of  these  elements 
emits  a  coloured  vapour;  each,  though  incombustible  in 
oxygen,  yet  forms  acids  with  it,  the  series  known  being  the 
following  :  — 

HF  —  —  — 

HC1         HC10         HC10,         HC103         HC1O4 
HBr        HBrO?  HBrO3         HBrO4 

HI  HIO3  HIO4v 

In  comparing  the  halogens  with  each  other,  the  chemical 
activity  of  fluorine,  which  has  the  smallest  atomic  weight,  is 
the  most  powerful  ;  next  in  the  order  in  activity  is  chlorine, 
then  bromine,  and,  lastly,  iodine,  the  atomic  weight  increas- 
ing as  the  chemical  energy  declines.  Chlorine  is  gaseous, 
bromine  liquid,  and  iodine  solid.  The  specific  gravity,  the 
fusing  point,  and  the  boiling  point,  rise  as  the  atomic  weight 
increases.  The  halogens  combine  energetically  with  the 
metals,  and,  when  united  with  the  same  metal,  furnish  com- 
pounds which  are  isomorphous  ;  that  is  to  say,  they  all  crys- 
tallise in  the  same  form  —  potassic  fluoride,  chloride,  bromide, 
and  iodide,  for  example,  all  crystallise  in  cubes. 


UNIVERSITY  OF  CALIFORNIA 


CHAPTER    VII. 

SULPHUR   GROUP. 

i.  SULPHUR.    2.  SELENIUM.     3.  TELLURIUM. 

^30)  i.  SULPHUR:  Symb.  S;  Atom.  Wt.  32;  Melting  Pt.* 
115°;  Boiling  Ft.  446°  C. 

Sulphur,  or  brimstone,  has  been  known  from  time  imme- 
morial, as  it  is  an  element  found  uncombined  in  considerable 
quantities  in  volcanic  districts.  It  is  also  found  in  com- 
bination with  many  of  the  metals ;  for  instance,  when  united 
with  iron  it  forms  the  yellow  brassy-looking  mineral  known 
as  iron  pyrites ;  with  lead  it  furnishes  galena,  the  principal 
ore  of  lead ;  and  with  zinc  it  gives  the  brown  mineral  called 
blende.  In  combination  with  oxygen,  it  is  found  forming 
salts  with  other  metals,  known  as  sulphates,  among  which 
those  of  calcium,  magnesium,  and  barium  are  of  most 
frequent  occurrence.  Sulphur  also  occurs  in  combination 
in  white  of  egg,  in  muscle,  and  some  other  animal  products. 

Sulphur  is  a  yellow  brittle  solid,  which  is  not  soluble  in 
water,  but  is  soluble  in  carbon  disulphide,  oil  of  turpentine, 
and  in  benzol,  as  well  as  to  a  slight  extent  in  hot  alcohol. 
It  is  highly  inflammable,  and  burns  with  a  blue  flame, 
emitting  pungent  suffocating  vapours  of  sulphurous  anhy- 
dride. When  heated  to  115°  C.  it  melts,  forming  a  trans- 
parent yellow  liquid,  which  undergoes  a  series  of  curious 
changes  by  the  continued  application  of  heat. 

Exp.  1 54. — Place  a  few  grams  of  sulphur  in  a  wide  test-tube, 
and  apply  the  heat  of  a  lamp  cautiously.  The  sulphur  melts 
and  forms  a  pale  yellow  liquid,  which  flows  easily.  Pour  part 
of  the  melted  mass  into  cold  water  :  a  yellow  brittle  solid  is 
formed.  Heat  the  portion  still  left  in  the  tube  more  strongly  : 
it  gradually  deepens  in  colour,  and  becomes  thick,  assuming  a 
treacly  appearance.  On  heating  the  sulphur  still  higher,  it  again 
becomes  somewhat  more  fluid.  Pour  it  now  in  a  thin  stream 
into  cold  water  :  the  sulphur  forms  into  tough,  elastic,  semi 
transparent  strings. 


142  Crystals  of  Sulphur. 

The  colour  of  these  cooled  threads  varies  from  a  pale 
amber  to  a  deep  brown,  becoming  darker  in  proportion  as 
the  heat  applied  is  greater.  If  kept  for  a  day  or  two,  this 
elastic  sulphur  gradually  becomes  hard,  opaque,  and  brittle. 

Sulphur  may  easily  be  obtained  in  crystals. 

Exp.  155. — Melt  from  a  quarter  to  half  a  kilogram  of  sulphur 
in  an  earthen  pipkin  at  a  low  and  carefully  applied  heat.  When 
completely  melted,  set  it  aside  to  cool  slowly.  Allow  it  to  stand 
for  a  short  time  after  it  has  become  solid  over  the  surface  ;  then, 
with  a  hot  wire,  pierce  two  holes  through  the  crust  near  the 
edge  on  opposite  sides,  and  pour  out  the  still  liquid  portion. 

When  the  mass  is  cold,  remove  the  solid  crust  carefully, 
and  the  interior  will  be  found  to  be  lined  with  transparent 
honey-yellow  needles,  which,  when  scratched,  or  even  when 
left  to  themselves  for  a  few  hours,  gradually  become  opaque. 
The  crystals  thus  obtained  belong  to  the  class  known  as  the 
oblique  prismatic. 

Sulphur  may  also  be  obtained  in  crystals  of  a  different 
form,  the  octahedron  with  a  rhombic  base.  Native  sulphur 
assumes  this  shape ;  and  it  may  be  obtained  by  dissolving 
sulphur  in  carbon  disulphide,  and  allowing  the  solution  to 
evaporate  spontaneously.  This  form  has  a  sp.  gr.  of  2  -05, 
while  the  crystals  obtained  by  fusion  (Exp.  155)  are  less 
dense,  being  only  of  sp.  gr.  1*98.  They  also  have  different 
fusing  points,  the  octahedral  sulphur  fusing  at  115°,  and  the 
prismatic  requiring  a  temperature  at  120°  C.  for  its  fusion. 

Bodies  which,  like  sulphur,  can  be  obtained  in  forms 
which  belong  to  two  distinct  classes  of  crystals  are  said  to 
be  dimorphous. 

Sulphur  also  offers  a  good  instance  of  allotropy.  In  these 
two  varieties  of  crystalline  form,  and  in  the  elastic  threads, 
or  viscous  state  obtained  by  sudden  cooling  from  a  high 
temperature,  we  have  three  different  modifications  of  the 
same  element.  A  fourth  may  also  be  procured  by  placing 
in  carbon  disulphide  the  hard  mass  furnished  by  keeping  the 
viscous  sulphur  till  it  becomes  solid.  The  carbon  disulphide 


Distillation  of  Sulphur. 


Fig.  60. 


dissolves  all  that  can  be  removed  from  the  mass,  and  a  grey 
amorphous  (or  non-crystalline)  powder  is  left;  this  differs 
from  the  crystalline  varieties  in  its  singular  insolubility  in 
carbon  disulphide,  which  dissolves  both  the  crystalline  forms 
readily. 

All  these  different  varieties  of  sulphur  may  be  distilled  by 
the  application  of  sufficient  heat,  provided  air  be  excluded, 
otherwise  they  would  take  fire.  The  distilled  sulphur  thus 
obtained  exhibits  no  difference 
in  properties,  whichever  allo- 
tropic  modification  may  have 
been  used. 

Exp.  156. — Place  a  few  pieces 
of  sulphur  in  a  Florence  flask. 
Cut  off  the  neck  of  a  second 
flask,  so  as  to  enable  the  neck 
of  the  first  flask  to  pass  into  the 
second,  as  shown  in  Fig.  60. 
Heat  the  flask  containing  the 
sulphur,  covering  the  upper  sur- 
face with  a  cone  of  thin  sheet 
iron,  to  keep  it  hot.  The  sul- 
phur first  melts,  then  boils,  and 
ultimately  distils  over  into  the 
second  flask. 

The  vapour  of  sulphur,  at 
temperatures  of  about  500°,  is 
96  times  as  heavy  as  that  of 
an  equal  volume  of  hydrogen  at 
the  same  temperature ;  but  if  the  sulphur  vapour  be  heated 
to  1000°  C.  it  becomes  expanded,  until  its  density  is  only 
32  times  that  of  hydrogen  at  the  same  temperature  and 
pressure. 

Selenium  and  tellurium  show  the  same  curious  exceptional 
effect  of  heat  upon  their  vapours. 

The  compounds  which  sulphur  forms  with  any  of  the  other 
elements  are  termed  sulphides,  or  sometimes  sulphurcts. 


144  Sulphur  and  Oxygen. 

Advantage  is  taken  of  the  volatility  of  sulphur  to  purify 
it  from  earthy  matters.  It  is  usually  distilled  roughly  on 
the  spot  where  it  is  found,  and  afterwards  purified  by  a 
second  more  careful  distillation.  The  roll  sulphur  of  com- 
merce is  obtained  by  pouring  the  melted  sulphur  into  cylin- 
drical wooden  moulds,  in  which  it  is  allowed  to  cool. 
Flowers  of  sulphur,  as  they  are  called,  occur  in  the  form  of 
a  harsh  yellow  crystalline  powder,  which  is  procured  by 
distilling  sulphur  slowly  into  a  large  brickwork  chamber,  where 
the  fumes  become  condensed  in  this  form.  If  distilled  more 
quickly,  the  brickwork  becomes  hot,  and  then  the  sulphur 
melts  and  runs  down  the  sides,  forming  a  solid  mass  as  it  cools. 

Sulphur,  from  its  ready  inflammability,  is  used  in  the  pre- 
paration of  matches.  Large  quantities  are  also  employed 
in  the  manufacture  of  gunpowder;  but  its  principal  con 
sumption  is  in  the  production  of  sulphuric  acid. 

Sulphur  combines  directly  with  many  of  the  metals,  and 
gives  out  much  heat  in  the  process. 

Exp.  157. — Mix  3  or  4  grams  of  copper  filings  with  half  their 
weight  of  flowers  of  sulphur,  and  heat  them  in  a  large  test-tube.  At 
a  temperature  a  little  above  the  melting-point  of  sulphur  the  two 
bodies  will  begin  to  unite,  and  a  bright  glow  will  spread  through 
the  mass.  When  the  tube  is  cold,  break  it  and  examine  the 
product.  A  substance  in  no  way  resembling  copper  or  sulphur 
will  be  found  :  it  consists  of  the  sulphide  of  the  metal. 

Two  compounds  of  sulphur  with  oxygen  are  known,  sul- 
phurous anhydride  (SO2)  and  sulphuric  anhydride  (SO3), 
both  of  which  furnish  important  acids  when  combined  with 
water.  There  are  also  other  acids  of  sulphur  containing 
oxygen  :  these  are  known  as  the  polythionic  series,  in  refer- 
ence to  the  multiple  proportion  in  which  sulphur  (0e7ov)  enters 
into  their  formation.  It  will  be  sufficient  merely  to  give  their 
formulae.  The  series  of  oxygen-sulphur  acids  is  as  follows — 


Hydrosulphurous  acid   H2SO2 
Sulphurous  acid  H2SO3 

Sulphuric  acid  H2SO4 

Hyposulphurous  acid    H2S2O3 


Dithionic  acid  H2S2O6 

Trithionic  acid  H2S3O6 

Tetrathionic  acid  H2S4O6 

Pentathionic  acid  .    H2S5O6 


Sulphurous  Anhydride.  145 

(31)  SULPHUROUS  ANHYDRIDE  (or  Sulphur  Dioxide)  : 
Symb.  SO2 ;  Atom,  and  Mol.  Wt.  64 ;  Atom,  and  Mol.  Vol. 
]  ;  Spec.  grav.  of  gas,  2*247  ;  Re^  Wt.  32  ;  Boiling  Pt. 
-io°C;  Melting  Pt.  -76°. 

Sulphur  burns  in  oxygen  with  a  lilac  flame,  and  produces 
a  permanent  gas,  which,  after  it  has  again  become  cool, 
occupies  the  same  bulk  as  the  original  oxygen,  but  it  has 
become  doubled  in  density.  Two  volumes  of  oxygen  unite 
with  one  volume  of  sulphur  vapour,  the  three  volumes  be 
coming  condensed  into  two — 

The  gas  so  produced  has  a  pungent  and  suffocating  odour  ; 
in  a  concentrated  form  it  cannot  be  breathed,  but  in  a  diluted 
state  it  excites  the  symptoms  of  a  common  cold.  It  is  trans- 
parent and  colourless,  is  not  inflammable,  and  immediately 
extinguishes  the  flame  of  burning  bodies.  Water  dissolves 
more  than  40  times  its  bulk  of  the  gas,  and  furnishes  sulphur- 
ous acid-  H2O  +  So2  =  H2SO3. 
The  solution  has  the  smell  and  taste  of  the  gas,  which 
readily  escapes  from  the  water  when  heated. 

Sulphurous  anhydride  is  usually  obtained  by  heating  sul- 
phuric acid  in  contact  with  a  metal,  such  as  copper  :  sul- 
phurous anhydride  comes  off,  while  water  and  cupric  sulphate 
are  formed— 

2H2SO4  +  Cu     =     CuSO4  +  SO2  +   2H2O. 

Ex  p.  158. — Place  about  5  grams  of  copper  clippings  in  a  flask 
provided  with  a  cork  and  bent  tube,  and  pour  upon  it  30  c.  c. 
of  oil  of  vitriol.  Heat  the  mixture  strongly,  and  collect,  by 
downward  displacement,  2  or  3  jars  of  the  gas  that  is  given  oft. 
Test  one  jar  with  a  piece  of  blue  litmus  paper :  the  blue  will 
immediately  be  reddened.  Plunge  a  lighted  taper  into  another 
jar  :  it  will  be  extinguished. 

Exp.  1 59. — Suspend  a  bunch  of  violets  or  a  rose  in  a  jar  ot 
the  gas  :  they  will  be  bleached  completely.  Throw  the  flowers 
into  a  very  weak  solution  of  ammonia  :  the  colour  will  first  be 
restored,  and  will  then  be  changed  to  green  by  the  alkali. 

L 


146  The  Sulphites. 

The  bleaching  action  of  this  gas  differs  from  that  of 
chlorine  in  not  destroying  the  colour,  for  this  is  again 
restored  by  the  action  of  an  alkali  or  a  stronger  acid. 

Flannel,  sponge,  silken  goods,  isinglass,  and  many  articles 
which  would  be  injured  by  chlorine,  are  bleached  by  suspend- 
ing them,  in  a  damp  state,  in  a  closed  chamber,  and  then  ex- 
posing them  to  the  fumes  of  burning  sulphur.  (See  Appendix.) 
Sulphurous  anhydride  is  useful  as  a  fumigation  for  destroy- 
ing infection.  By  its  action,  meat  is  also  preserved  from 
putrefying  for  a  while  ;  and  it  is  frequently  employed  to  check 
fermentation  in  cider  and  home-made  wines,  for  which  pur- 
pose a  little  sulphur  is  burnt  in  the  cask  before  filling  it  with 
the  liquor. 

There  are  various  other  modes  of  obtaining  the  gas.  One 
of  these  consists  in  heating  a  mixture  of  powdered  black 
manganese  oxide  with  about  its  own  weight  of  sulphur ;  half 
the  sulphur  combines  with  the  oxygen,  the  other  half  with 
the  manganese — 

MnO2  +  Sa     =     MnS  +  SO2. 

If  charcoal  is  boiled  with  sulphuric  acid,  a  mixture  of  sul- 
phurous and  carbonic  anhydrides  are  evolved — 

C  +  2H2SO4  =  2SO2  +  CO2  +  2H2O. 
In  the  manufacture  of  sulphuric  acid,  sulphurous  anhydride 
is  supplied  simply  by  burning  sulphur  or  iron  pyrites  in  a 
current  of  air.  In  this  way  it  is  obtained  mixed  with  a  large 
bulk  of  nitrogen.  Sulphurous  anhydride  is  also  emitted 
largely  from  the  craters  of  volcanoes. 

When  dissolved  in  water,  the  gas  furnishes  sulphurous 
acid,  and  this  acid  furnishes  the  salts  known  as  sulphites. 
The  sulphites  of  the  alkalies  may  be  obtained  by  passing  the 
gas  into  a  solution  of  potash  or  soda.  It  forms  two  kinds  of 
salts  :  one  of  these  contains  two  atoms  of  the  metal,  such  as 
the  common  disodic  sulphite  (Na2SO3,  ioH2O),  while  the 
other  kind  of  salt  is  frequently  called  a  bisulphite,  and  con- 
tains but  a  single  atom  of  the  metal.  Hydric  potassic 
sulphite  (KHSO3)  is  the  best  example  of  this  class. 


Sulphuric  Acid.  147 

The  sulphites  are  easily  distinguished  by  their  effervescing 
when  treated  with  a  strong  acid,  such  as  the  hydrochloric, 
giving  off  a  colourless  gas,  with  the  pungent  characteristic 
odour  of  sulphurous  anhydride. 

Exp.  1 60. — Add  a  little  of  a  solution  of  baric  chloride  to  a 
solution  of  a  sulphite.  A  white  precipitate  of  baric  sulphite 
(BaSO3)  is  formed. 

In  this  case,  if  the  sulphite  be  free  from  sulphate,  the  pre- 
cipitate will  be  dissolved  on  adding  a  little  hydrochloric 
acid  ;  but  the  clear  liquid  will  be  rendered  milky  by  the 
addition  of  chlorine  water,  which  will  convert  the  sulphurous 
into  sulphuric  acid,  and  this  will  give  a  white  precipitate  of 
baric  sulphate,  which  is  insoluble  in  acids. 

The  chlorine  takes  hydrogen  from  the  water,  forming 
hydrochloric  acid,  and  the  oxygen  which  is  set  free  converts 
the  sulphurous  into  sulphuric  acid — 

H2SO3  +  Cla  +  H2O     =     H2SO4  +  *HCL 

(32)  SULPHURIC  ACID  (Dihydric  Sulphate) :  Symbol, 
H2SO4;  Mol.  Wt.  98;  Sp.  grav.  of  liquid,  1-846-;  Melting 
Pt.  10-5°  C.;  Boiling  Pt.  338°. 

This  is  the  most  important  of  the  acids,  and  is  the  basis 
of  our  chemical  manufactures.  The  consumption  of  it 
annually  in  this  country  considerably  exceeds  100,000  tons', 
or  one  hundred  million  kilograms. 

Exp.  161. — Dry  some  of  the  green  crystals  of  ferrous  sulphate 
(the  salt  formerly  called  green  vitriol},  and  place  the  dried  salt 
in  a  test-tube,  and  heat  it  nearly  to  redness.  White  acid  fumes 
are  given  off,  which  condense  in  oily-looking  drops ;  they  are 
mixed  with  the  pungent  vapours  of  sulphurous  anhydride. 
When  all  the  acid  is  expelled,  a  red  powder,  consisting  of  ferric 
oxide,  or  colcothar,  as  it  is  called,  is  left  in  the  tube. 

The  changes  may  be  thus  represented — 

2FeSO4     =     Fe2O3    +    SO3    +    SO2. 

From  the  oily  appearance  of  the  product  the  old  name  of 
oil  of  vitriol  was  derived. 

L  2 


148  Formation  of  Sulphuric  Anhydride. 

When  thus  prepared,  the  distilled  liquid  consists  of 
a  mixture  of  sulphuric  acid  with  sulphuric  anhydride 
(H2SO4,  SO3).  Some  sulphuric  acid  is  always  formed 
during  the  operation,  because  the  ferrous  salt  cannot  in 
practice  be  completely  freed  from  water  before  it  is  distilled. 
This  water  comes  away  during  distillation  ;  and  as  soon  as 
the  anhydride,  which  distils  off  also,  becomes  mixed  with 
water,  combination  between  the  two  occurs,  and  sulphuric 
acid  is  formed,  SO3-f  H2O  becoming  H2SO4. 

The  distillation  of  dried  sulphate  of  iron  has  long  been 
conducted  on  a  considerable  scale  at  the  town  of  Nord- 
hausen,  in  Saxony,  where  it  is  made  for  the  purpose  of  dis- 
solving indigo  for  the  preparation  of  Saxony  blue,  and  hence 
the  acid  so  prepared  is  generally  called  Nordhausen  Sulphuric 
Add.  When  such  sulphuric  acid,  holding  sulphuric  anhy- 
dride in  solution  (H2SO4,  SO3),  is  heated,  the  sulphuric 
anhydride  (SO3)  comes  off  in  dense  white  fumes,  which,  if 
immediately  shut  up  in  a  vessel  excluded  from  the  moisture 
of  the  air,  become  -converted,  as  it  cools,  into  a  silky-looking 
white  fibrous  mass.  This  substance  is  not  acid,  though  it 
immediately  becomes  so  when  mixed  with  water.  It  com- 
bines with  water  with  the  production  of  a  very  high  tempera- 
ture, emitting  a  hissing  sound,  like  that  produced  by 
quenching  a  red-hot  body  in  water.  After  the  water  has 
thus  combined  with  the  anhydride  the  two  are  not  separated 
readily  by  simple  heat.  If  the  acid  thus  obtained  be  further 
diluted  with  water,  this  additional  quantity  of  water  may  be 
removed  by  evaporation.  During  this  process  the  boiling 
point  gradually  rises  till  it  reaches  338°;  when  this  point  is 
attained,  the  acid  has  become  reduced  to  the  state  repre- 
sented by  the  formula  H2SO4 ;  the  whole  then  distils  over, 
and  condenses  again  unaltered. 

The  great  bulk  of  the  sulphuric  acid  required  in  the  arts 
is,  however,  obtained  by  a  different  process  from  that  just 
described.  When  sulphur  is  burned  in  dry  air  or  in  oxygen, 
the  product  is  always  sulphurous  anhydride ;  it  never  occurs 


Sulphuric  Acid  Chamber.  149 

as  a  higher  state  of  oxidation  of  sulphur,  although  a  higher 
oxide — namely,  the  sulphuric  anhydride — may  be  obtained  by 
indirect  means.  If  sulphurous  anhydride  be  mixed  with  oxygen 
in  the  presence  of  water,  and  be  presented  to  nitric  oxide, 
or  to  any  other  of  the  higher  oxides  of  nitrogen,  the  further 
oxidation  of  the  sulphur  may  be  effected  with  great  rapidity. 
Moreover,  a  small  proportion  of  the  oxide  of  nitrogen  will 
effect  the  combination  of  an  indefinite  amount  of  sulphurous 
anhydride  and  oxygen.  Nitric  oxide  (NO)  in  the  presence 
of  oxygen  immediately  becomes  nkrogen  peroxide  (NO2), 
and  this,  when  mixed  with  sulphurous  anhydride  and  a  large 
quantity  of  water,  furnishes  sulphuric  acid  and  nitric  oxide. 
The  sulphuric  acid  remains  dissolved  in  the  water,  while  the 
nitric  oxide,  by  absorbing  oxygen  from  the  air,  again  becomes 
nitrogen  peroxide;  this  combines  with  fresh  sulphurous 
anhydride,  which,  when  acted  on  by  water,  becomes  sul- 
phuric acid,  the  nitric  oxide  being  again  liberated,  to  go 
through  the  same  series  of  changes  with  fresh  portions  of 
oxygen  and  sulphurous  anhydride  as  long  as  any  remain  in 
presence  of  each  other  uncombined,  NO2  +  SO2  +  oc  H2O 
yielding  NO  +  H2SO4  +  x  -iH2O. 

In  making  sulphuric  acid  on  a  large  scale,  sulphur  or  iron 
pyrites  is  burned  in  a  current  of  air  in  furnaces  (A  A,  Fig.  61). 
In  the  stream  of  heated  gas  is  suspended  an  iron  pot  (b\ 
charged  with  a  mixture  of  sodic  nitrate  and  sulphuric  acid. 
Vapours  of  nitric  acid  are  thus  set  free,  and  these  pass  on 
mixed  with  sulphurous  anhydride  and  excess  of  atmospheric 
air.  The  mingled  gases  pass  into  immense  chambers  (F  F), 
constructed  of  sheet  lead,  supported  by  a  framework  of 
timber.  A  shallow  layer  of  water  (d]  covers  the  bottom  of 
the  chamber,  and  the  intermixture  and  chemical  action  of 
the  gases  are  further  favoured  by  the  injection  of  jets  of 
steam  (eee),  supplied  from  the  boiler  (G).  (See  Appendix.) 
The  vapours  of  nitric  acid  lose  part  of  their  oxygen,  and  are 
quickly  reduced  by  the  sulphurous  acid  to  the  state  of  nitric 
oxide  ;  then  the  changes  already  described  succeed  each 


ISO 


Properties  of  Sulphuric  Acid. 


other  rapidly,  leaving  ultimately  nothing  but  nitrogen  and 
nitric  oxide,  which  pass  off  into  the  atmosphere  by  a  flue  (c). 
Fig.  61. 


The  sulphuric  acid  which  collects  at  the  bottom  of  the 
chamber  is  concentrated  by  evaporation  in  shallow  leaden 
pans,  till  it  reaches  a  sp.  gr.  of  1720,  when  it  forms  the 
brown  sulphuric  acid  of  commerce.  In  this  state  it  is  largely 
employed  in  making  manures,  and  for  converting  common 
salt  into  sodic  sulphate.  The  further  concentration  must  be 
completed  in  glass  or  platinum  stills,  as  the  leaden  pans 
would  melt  at  the  heat  required.  In  these  it  is  further 
evaporated  till  the  boiling  point  has  risen  to  338°  C.,  and 
then  nothing  but  the  concentrated  acid  (H2SO4)  remains. 
If  the  application  of  heat  were  continued  further,  the  acid 
would  distil  over. 

The  oil  of  vitriol  of  commerce  is  a  dense  oily-looking 
colourless  liquid,  without  odour,  and  of  sp.  gr.  1-842.  It  is 
intensely  caustic,  and  chars  almost  all  organic  substances, 
owing  to  its  powerful  attraction  for  moisture.  If  exposed  in 
a  shallow  dish  to  the  air  for  a  few  days,  it  increases  in  weight 
considerably,  by  absorbing  watery  vapour  from  the  air.  This 
property  may  be  made  use  of  for  the  purpose  of  drying 
gases  and  various  other  bodies  in  the  laboratory.  When 


Salts  of  Sulphuric  Acid.  151 

mixed  with  water,  it  gives  out  great  heat,  so   that  much 
care  is  required  in  diluting  the  acid. 

Exp.  162. — Pour  a  little  of  the  strong  acid  into  a  test-tube. 
Place  a  splinter  of  wood  in  it  :  the  wood  will  be  blackened  in  a 
few  minutes. 

Exp.  163. — Pour  a  cub.  centim.  of  the  strong  acid  into  a  tube 
containing  3  or  4  c.  c.  of  water  :  considerable  heat  will  be  felt 
to  attend  the  mixture.  Take  a  little  of  this  diluted  acid,  and 
with  a  feather  dipped  into  it  trace  a  few  letters  upon  writing- 
paper.  Hold  the  paper  near  the  fire  :  the  water  will  evaporate, 
leaving  the  acid  behind  ;  this  will  soon  blacken  the  paper. 

It  is  owing  to  this  kind  of  action  that  even  a  very  dilute 
acid,  if  left  upon  linen,  will  cause  it  to  fall  into  holes  when 
exposed  to  the  air;  the  water  evaporates,  and  the  acid, 
which  is  not  volatile,  destroys  the  fibre. 

Tests. — The  sulphates,  when  dissolved  in  water,  may  be 
known  by  producing  a  white  precipitate  when  mixed  with  a 
solution  of  a  salt  of  barium,  such  as  baric  chloride.  This 
precipitate  consists  of  baric  sulphate  (BaSO4).  It  is  not 
dissolved  by  nitric  acid. 

The  sulphuric  belongs  to  the  class  of  acids  known  as 
dibasic ;  that  is  to  say,  it  contains  two  atoms  of  hydrogen, 
which  admit  of  displacement  by  a  metal ;  and,  like  all  acids  of 
this  class,  it  furnishes  two  sets  of  salts  with  metals  of  which 
the  atom,  like  the  sulphides  of  the  alkali-metals,  is  chemically' 
equivalent  to  one  atom  of  hydrogen.  Such  metals  are  called 
monads.  In  one  set  of  these  salts  one  atom  only  of  hydro- 
gen is  displaced  by  the  metal,  in  the  other  set  both  atoms 
of  hydrogen  are  so  displaced.  A  salt  of  the  first  series  is 
often  spoken  of  as  an  acid  salt ;  for  instance,  they  may  be 
thus  represented,  if  the  formula  of  sulphuric  acid  be  written 
as  dihydric  sulphate  (H2SO4);  then — 

Hydric  potassic  sulphate,  is  HKSO4 ; 
Dipotassic  sulphate,  or  normal  sulphate,  K2SO4. 

But  there  are  cases  in  which  a  single  atom  of  a  metal,  like 
calcium,  displaces  both  atoms  of  the  hydrogen,  and  then 


152  Sodic  Hyposulphite. 

but  one  salt  of  such  metal  can  be  formed.  Copper,  lead,  and 
barium  are  metals  of  this  kind.  These  metals,  of  which  the 
atom  is  thus  equivalent  chemically  to  two  atoms  of  hydrogen, 
are  called  dyads ;  so  that  we  write — 

Baric  sulphate  Ba"SO4 

Calcic  sulphate  Ca"SO4 

Lead  sulphate  Pb"SO4 

and  so  on.  The  two  dashes  ("),  when  used,  imply  that  the 
metal  has  supplied  the  place  of  two  atoms  of  hydrogen. 

Lead  sulphate  is  nearly  as  insoluble  as  baric  sulphate,  and 
strontic  sulphate  is  but  little  less  so.  Calcic  sulphate  is 
more  soluble,  though  still  but  slightly  so ;  but  most  of  the 
other  sulphates  are  freely  soluble.  The  soluble  sulphates 
are  often  easily  formed  by  dissolving  the  metal  in  dilute 
sulphuric  acid  ;  where  this  cannot  be  done,  the  oxide  or  the 
carbonate  of  the  metal  may  be  dissolved  in  the  acid — 
(i)Zn  +  H3SO4  =  ZnSO4  +  H,, 

(2)  CuO         +   HaSO4   =   CuSO4     +   HZO;  or 

(3)  MnCO3   +   HZSO4   =   MnSO4    +   HaO   +   CO,. 

(33)  Hyposulphites. — Sodic  hyposulphite  is  a  salt  which 
is  used  extensively  by  the  photographer.  This  use  depends 
upon  the  fact  that  the  hyposulphite  has  the  power  of  dis- 
solving many  of  the  salts  of  silver  which  are  insoluble  in 
water. 

Exp.  164. — Add  a  solution  of  sodic  hyposulphite  to  some 
freshly  precipitated  argentic  chloride  (p.  276) ;  the  latter  will  be 
completely  dissolved  owing  to  the  formation,  by  double  decom- 
position, of  argentic  sodic  hyposulphite  readily  soluble  in  water- 

NaaSaO3   +   AgCl     =     AgNaSaO,   +    NaCl. 

Argentic  bromide  and  argentic  iodide  may  also  be  dis 
solved  by  the  hyposulphite,  though  not  so  readily. 

When  a  photograph  is  washed  in  water,  the  excess 
soluble  argentic  nitrate  is  washed  out,  but  the  chloride  of 
iodide  remains  in  the  paper.  If  now  this  be  plunged  into  a 
solution  of  sodic  hyposulphite,  the  portion  of  unaltered  in- 
soluble silver  salt  becomes  dissolved  in  the  liquid,  while  the 


Sulphuretted  Hydrogen. 


153 


part  which  has  been  blackened  by  light  is  unacted  on.  If 
the  picture  is  then  thoroughly  washed  in  pure  water  it  is 
fixed  \  that  is,  it  becomes  no  longer  liable  to  change  on 
exposure  to  light. 

There  are  several  ways  of  preparing  sodic  hyposulphite. 
One  of  the  simplest  consists  in  digesting  a  solution  of  sodic 
sulphite  upon  flowers  of  sulphur — 

Na2SO3  +  S     =     Na2S2O3. 

A  colourless  solution  is  obtained,  from  which,  on  evapora- 
tion, large  colourless  striated  crystals  of  sodic  hyposulphite 
are  easily  procured  (Na2S2O3,  5H3O).  Many  other  hypo- 
sulphites may  be  obtained,  but  they  are  unimportant.  The 
acid  cannot  be  isolated,  as  it  immediately  begins  to  undergo 
decomposition  into  sulphur  and  sulphurous  acid. 

Exp.  165. — Add  to  a  solution  of  sodic  hyposulphite  a  little 
hydrochloric  acid.  In  a  few  minutes  a  pungent  smell  of  sul- 
phurous acid  will  be  perceived,  while  the  liquid  becomes  milky 
from  the  deposition  of  sulphur — 

NaaS203+  2HC1     =     2NaCl  +   H,SO3   +   S. 

(34)  SULPHURETTED  HYDROGEN  :  Symb.  H2S ;  Atomic  and 
Mol.  Wt.  34;  Mol.  Vol.  pH;  Sp.  Gr.  1-1912;  Relative 
Wt.  17. 

Exp.   166.— Place    10  or  15  Fig.  62. 

grams  of  ferrous  sulphide  in 
small  lumps  in  a  gas  bottle 
(Fig.  62),  and  pour  upon  it 
about  100  c.  c.  of  diluted  sul- 
phuric acid  (i  of  acid  to  6  of 
water)  :  an  effervescence,  with 
escape  of  this  offensive  gas, 
immediately  occurs — 
H2SO4  +  FeS  =  FeSO4+  H2S. 

Other  sulphides  also  furnish 
the  gas  —  sulphide   of  anti- 
mony, for  example,   when  heated  with  hydrochloric  acid. 
This  gas  is  often  wanted  in  the  laboratory  for  the  analysis 


154  Sulphuretted  Hydrogen. 

of  ores,  and  Fig.  62  shows  a  convenient  mode  of  arranging 
the  apparatus  for  liberating  it.  The  small  bottle  contains  a 
little  water,  through  which  the  gas  bubbles,  in  order  to  re- 
move any  particles  of  acid  or  of  iron  salt  which  may  have 
been  splashed  over  by  the  effervescence,  before  it  is  passed 
into  the  solution  for  analysis. 

Sulphuretted  hydrogen  is  colourless  and  transparent ;  it 
has  a  disgusting  odour  of  rotten  eggs,  and  is  very  poisonous 
if  breathed.  It  is  soluble  in  about  one-third  of  its  bulk  of 
water,  and  the  solution,  which  has  the  smell  of  the  gas,  is  a 
useful  test  for  certain  metals.  But  if  the  solution  be  kept  in 
bottles  only  partially  filled,  the  oxygen  of  the  air  combines 
with  the  hydrogen  of  the  compound,  water  is  formed,  and 
the  liquid  becomes  milky  from  deposited  sulphur — 
2H2S  +  O2  =  2H2O  +  S2. 

Sulphuretted  hydrogen  burns  in  the  air  with  a  pale  bluish 
flame,  furnishing  water  and  sulphurous  anhydride.  It  con- 
tains its  own  bulk  of  hydrogen,  and  half  its  volume  of  the 
vapour  of  sulphur — 

the  three  volumes  of  the  constituents  becoming  condensed 
into  two  volumes,  just  as,  in  the  analogous  case  of  water,  the 
two  volumes  of  hydrogen  and  one  volume  of  oxygen  furnish 
two  volumes  of  steam. 

Sulphuretted  hydrogen,  though  soluble,  may  be  collected 
over  warm  water,  if  the  gas  be  made  in  a  retort  or  in  a  flask 
fitted  with  a  gas  tube. 

Exp.  167. — Fill  two  small  bottles  of  250  or  300  c.  c.  capacity 
with  the  gas;  prepare  a  bottle  of  sulphurous  anhydride  of 
similar  size;  withdraw  the  stopper,  and  close  the  bottle  with  a 
glass  plate.  Do  the  same  with  one  of  the  bottles  of  sulphuretted 
hydrogen,  and  invert  the  sulphurous  anhydride  over  this  bottle. 
The  two  gases  will  immediately,  in  the  presence  of  the  moisture, 
react  on  each  other ;  the  oxygen  of  the  sulphurous  anhydride 
uniting  with  the  hydrogen  of  the  sulphuretted  hydrogen,  while 
sulphur  is  deposited. 


Hydrosulphates.  155 

A  little  pentathionic  acid  (H2S5C>6)  is  always  formed  at 
the  same  time — 

5H2S  +  sSO2     =     58  +  4H2O  +  H2S5O6. 
Chlorine,  iodine  and  bromine  also  immediately  decompose 
sulphuretted  hydrogen,  with  separation  of  sulphur. 

Exp.  1 68. — Repeat  the  experiment  above  described,  substitu- 
ting a  bottle  of  chlorine  for  one  of  sulphurous  anhydride  :  hydro- 
chloric acid  is  formed,  and  sulphur  is  deposited — 
H,S    +    Q,     =     2HC1   +   S. 

Sulphuretted  hydrogen  is  often  produced  spontaneously 
under  various  circumstances.  Whenever  a  soluble  sulphate 
of  the  metal  of  one  of  the  alkalies  or  alkaline  earths  is  kept 
in  contact  with  decaying  organic  matter,  where  air  does  not 
find  free  access,  the  sulphate  becomes  reduced  to  the  form 
of  sulphide,  so  that  soluble  sulphides  become  formed,  the 
organic  matter  removing  the  oxygen  and  furnishing  water 
and  carbonic  acid.  The  deoxidising  action  on  sodic  sul- 
phate is  as  follows  : 

Na2SO4  -  2O2     =     Na2S. 

In  this  way  soluble  sulphides  are  formed  in  certain 
springs,  such  as  those  of  Harrogate  and  Moffat,  giving  to 
them  their  nauseous  odour ;  since  the  sulphuretted  hydrogen 
is  liberated  by  the  action  of  even  so  feeble  an  acid  as  the 
carbonic — 

Na2S  +  H20   +   CO2     =     Na2CO3  +  H2S. 

Owing  to  the  great  tendency  of  sulphur  to  unite  with 
metals  the  hydrogen  in  sulphuretted  hydrogen  may  be  rea- 
dily replaced  by  metals  forming  sulphydrates  or  sulphides. 
Thus  if  the  gas  be  passed  into  a  solution  of  potash  it  is 
quickly  absorbed  and  potassic  sulphydrate  is  produced — 

KHO   +   H2S     =     KHS   +   H2O. 

Since,  however,  potassic  sulphydrate  and  potassic  hydrate 
react  to  form  potassic  sulphide  and  water  (KHS  +  KHO 
=  K2S  +  H2O),  the  solution  if  only  half  saturated  with 
sulphuretted  hydrogen  contains  potassic  sulphide. 


156        Sulphuretted  Hydrogen  and  the  Metals. 

A  solution  of  ammonia,  when  saturated  with  sulphuretted 
hydrogen,  is  a  useful  test  for  metals,  2H3N  +  H2S  yielding 
(H4N)2S. 

Metals  the  atom  of  which,  like  potassium,  take  the  place 
of  a  single  atom  of  hydrogen  usually  form  two  compounds 
with  sulphuretted  hydrogen,  in  one  of  which  a  single  atom 
of  the  hydrogen  is  displaced  by  the  metal,  and  in  the  other 
both  atoms  are  displaced ;  for  instance,  we  have — 
Sulphuretted  hydrogen  H  H  S 

Hydric  potassic  sulphide  KHS 

Dipotassic  sulphide  KKS ; 

whilst  metals  of  which  the  atom,  like  calcium,  displaces  two 
atoms  of  hydrogen  form  but  a  single  compound  when  acted 
upon  by  the  gas  ;  as,  for  example — 

Baric  sulphide  BaS, 

Calcic  sulphide  CaS ;  and  so  on. 

Certain  metals  may  be  precipitated  from  their  acidulated 
solutions  by  sulphuretted  hydrogen.  Among  these  are  silver, 
bismuth,  mercury,  lead,  copper,  gold,  platinum,  tin,  antimony, 
and  arsenicum ;  and  the  precipitate,  which  is  usually  in  the 
form  of  a  hydrate,  often  has  a  characteristic  colour. 

Exp.  169. — Prepare  a  solution  of  sulphuretted  hydrogen  in 
water,  by  passing  a  stream  of  bubbles  of  the  gas  through 
water  for  a  few  minutes.  Add  some  of  this  solution  to  a  dilute 
solution  of  tartarised  antimony  :  a  beautiful  orange-coloured 
antimony  sulphide  is  separated.  With  a  dilute  solution  of 
stannic  chloride,  a  yellow  stannic  sulphide  will  be  formed  ;  and 
with  a  solution  of  cupric  sulphate,  also  largely  diluted,  a 
brownish-black  cupric  sulphide  will  be  obtained. 

Other  metals  are  not  precipitated  from  the  acidulated 
solutions  of  their  salts  by  sulphuretted  hydrogen  ;  among 
these  are  the  salts  of  iron,  cobalt,  nickel,  manganese,  zinc, 
aluminum,  and  chromium.  Hence  it  is  customary,  in  the 
analysis  of  minerals,  to  employ  sulphuretted  hydrogen  as  a 
means  of  separating  those  metals  above  mentioned  which 
are  precipitated  from  their  solutions  by  the  action  of  the 
gas  from  those  which  are  unacted  upon  by  it. 


Carbon  Bisulphide.  157 

In  the  case  of  those  metals  which  are  not  precipitated 
from  their  acid  solutions  by  sulphuretted  hydrogen,  the  sul- 
phide may  generally  easily  be  obtained  by  presenting  an 
alkali  metal  to  the  acid  radical  at  the  same  moment  that 
the  sulphur  is  presented  to  the  metal  which  is  required  in 
the  state  of  insoluble  sulphide,  and  this  is  done  by  adding  a 
soluble  sulphide  to  the  solution  of  the  metallic  salt.  Ferrous 
sulphate,  for  instance,  gives  no  precipitate  with  sulphuretted 
hydrogen,  but  it  yields  a  black  ferrous  sulphide  as  soon  as 
its  solution  is  mixed  with  one  of  dipotassic  sulphide — 
FeSO4  +  K2S  =  K2SO4  +  FeS. 

Many  of  the  sulphides  of  metals  which  are  precipitated  by 
the  gas  from  the  acid  solutions  of  their  salts  are  soluble  in 
the  solutions  of  the  alkaline  sulphides,  owing  to  their  power 
of  forming  double  sulphides,  which  are  soluble  in  water. 
Among  these  are  the  sulphides  of  gold,  platinum,  antimony, 
arsenicum,  and  tin,  which  may  be  dissolved  out  and  separated 
from  other  sulphides  such  as  those  of  copper,  bismuth,  lead, 
silver  and  mercury,  by  treating  the  mixed  precipitates  with  a 
solution  of  dipotassic  sulphide,  in  which  the  metals  last 
enumerated  are  insoluble. 

The  smell  of  sulphuretted  hydrogen  is  one  of  its  several 
tests ;  very  small  traces  of  it  may  also  be  recognised  by 
their  power  of  blackening  white  paper  moistened  with  a 
solution  of  acetate  or  other  salt  of  lead. 

Exp.  170. — Place  a  drop  of  a  solution  of  lead  acetate  upon  a 
piece  of  paper.  Hold  it  for  an  instant  near  the  open  bottle  of  a 
solution  of  sulphuretted  hydrogen  :  a  black  or  brown  stain  of 
lead  sulphide  will  immediately  be  produced. 

(35)  CARBON  BISULPHIDE:  Symb.  CS2;  Atomic  Wt.  76, 
— This  is  an  extremely  volatile  liquid,  usually  of  very 
offensive  odour,  due  to  some  impurity.  It  exerts  a  poisonous 
action  upon  animals.  It  boils  at  48°,  giving  off  a  remarkably 
inflammable  vapour.  It  is  considerably  heavier  than  water, 
and  is  not  soluble  in  it ;  but  is  very  soluble  in  ether  and 


158  Selenium  and  Tellurium. 

alcohol,  as  well  as  in  the  oils.  It  is  one  of  the  best  solvents 
for  the  oils  and  fats,  and  is  used  largely  for  their  extraction.  It 
also  freely  dissolves  sulphur,  iodine,  bromine,  and  phos- 
phorus. 

Exp.  171. — Place  a  few  drops  of  the  di sulphide  in  three  or  four 
test-tubes.  To  one  add  a  little  powdered  sulphur,  to  a  second  a 
minute  scrap  of  iodine,  to  a  third  a  fragment  of  phosphorus,  and 
to  a  fourth  a  few  drops  of  water.  Notice  the  beautiful  colour 
produced  by  the  iodine,  the  solution  of  the  sulphur  and  phos- 
phorus, and  the  insolubility  of  the  liquid  in  water. 

Carbon  disulphide  is  prepared  on  a  large  scale  by  driving 
the  vapour  of  sulphur  over  glowing  coke,  and  condensing 
that  vapour  in  suitably  cooled  receivers.  It  is  one  of  the 
few  liquids  which  does  not  freeze  at  the  lowest  temperature 
hitherto  obtained.  This  body  combines  with  the  sulphides 
of  the  alkali  metals,  and  forms  unstable  compounds,  which 
are  in  some  respects  analogous  to  the  carbonates,  but  they 
contain  sulphur  instead  of  oxygen ;  K2CO3  being  the  car- 
bonate, K2CS3  the  corresponding  sulphocarbonate. 

Sulphur  combines  with  chlorine  in  two  proportions.  One 
of  these  (S2C12)  is  a  yellow  liquid,  the  other  (SC12)  is  of  a 
deep  red  colour,  and  fumes  strongly  in  the  air.  Both  are 
decomposed  by  water. 

2.  SELENIUM.     3.  TELLURIUM. 

Sulphur  belongs  to  a  group  of  elements  of  which  the  other 
two,  selenium  and  tellurium,  are  of  rare  occurrence,  and  are 
practically  unimportant.  All  three  elements  are  characterised 
by  forming  gaseous  fetid  compounds  with  hydrogen,  con- 
taining two  atoms  of  hydrogen  to  one  atom  of  the  charac- 
teristic element,  and  in  each  case  the  gas  contains  two 
volumes  of  hydrogen  united  with  one  volume  of  the  vapour 
of  the  other  element,  the  three  volumes  having  become  con- 
densed into  the  space  of  two. 

All  the  three  elements  have  a  strong  attraction  for  oxygen, 
and  they  each  furnish  two  oxidized  compounds,  which  in 
combination  with  water  have  acid  properties. 


The  Phosphorus  Group. 

Sulphuretted  hydro-  Sulphurous  acid  Sulphuric  acid 
gen  (H,S)                      (H2S03)  (HaSO4) 

Seleniuretted  hydro-  Selenious  acid  Selenic  acid 
gen  (H,Se)                    (HaSeO3)  (H2SeO4) 

Telluretted     hydro-  Tellurous  acid  Telluric  acid 
gen  (HaTe)                    (H,TeO3)  (HaTeO4) 

The  properties  of  selenium  are  intermediate  between  those 
of  sulphur  and  tellurium  ;  and  this  last  has  so  much  resem- 
blance to  the  metals  that  it  is  usually  described  among  them. 
Of  the  three,  sulphur  has  the  lowest  and  tellurium  the  highest 
atomic  weight ;  and  the  specific  gravity,  the  fusing  point, 
and  the  boiling  point  increase  in  the  same  order  as  the 
atomic  weights. 


CHAPTER    VIII. 

PHOSPHORUS   GROUP. 
i.  PHOSPHORUS.     2.  ARSENICUM.    3.  ANTIMONY.    4.  BISMUTH. 

(36)  i.  PHOSPHORUS:  Symb.  P;  Atom.  Wt.  31;  Atom. 
Vol.  []  ;  Sp.  gr.  of  solid,  1*83  ;  of  vapour,  4*42  ;  Rel.  Wt. 
62;  Mol.  Wt.  P4,  124;  Mol.  Vol.  [7TT1  ;  Boiling  ^.288° ; 
Fusing  Pt.  44°. 

This  remarkable  element  has  considerable  resemblance  to 
be  metals  arsenicum  and  antimony.  All  three  form  fetid, 
nnammable,  gaseous  compounds  with  hydrogen,  in  which 
dree  atoms  of  hydrogen  are  united  with  one  atom  of  the 
other  element.  Nitrogen  has  also  a  near  relation  to  this 
group ;  but  its  hydrogen  compound,  ammonia,  is  strongly 
alkaline,  while  the  hydrogen  compounds  of  the  other  mem- 
bers of  the  group  are  very  feebly  so.  Bismuth,  though  a 
member  of  this  group,  forms  no  compound  with  hydrogen. 
Each  of  the  five  elements  is  also  distinguished  by  furnishing 
two  compounds  with  oxygen,  which,  when  combined  with 
water,  possess  acid  properties,  except  the  lower  compound 


1 60  Sources  of  Phosphorus. 

with  antimony,  which  is  feebly  basic,  and  that  of  bismuth, 
which  is  more  strongly  basic. 

Ammonia  Nitrous  anhydride        Nitric  anhydride 

(NH3)  (N203)  (Na05) 

Phosphuretted  hy-      Phosphorous  anhy-       Phosphoric  anhy- 

drogen  (PH3)  dride  (PaO3)  dride  (P2O5) 

Arseniuretted  hydro-   Arsenious  anhydride    Arsenic  anhydride 

gen(AsH3)  (As,O3)  (AsaO5) 

Antimoniuretted  hy-    Antimonious  anhy-       Antimonic  anhy- 

drogen  (SbH3)  dride  (SbaO3)  dride  (Sb2O5) 

Bismuth  oxide        Bismuthic  anhydride 
(Bi,03)  (Bi,05). 

Arsenicum,  antimony,  and  bismuth  will  be  described  with 
the  metals. 

Phosphorus  is  never  found  uncombined  in  nature.  It 
occurs  in  small  quantities  in  granite  and  the  older  rocks,  in 
the  form  of  tricalcic  phosphate,  or  phosphate  of  lime.  When 
these  rocks  crumble  down  and  form  soil,  they  supply  phos- 
phates to  plants,  which  store  them  up  in  considerable  quantity 
in  their  seeds.  From  the  seeds  the  animals  which  feed  upon 
them  derive  a  sufficient  quantity  for  their  support.  Phosphorus 
collects  in  the  animal  system  in  large  quantities,  and  fur- 
nishes, as  calcic  phosphate,  the  principal  earthy  component 
of  the  bones.  Phosphorus  is  also  an  essential  ingredient  in 
the  brain  and  nervous  tissue ;  and  it  passes  out  of  the  body 
constantly,  in  the  form  of  soluble  phosphates  in  the  urine, 
and  in  the  solid  excreta  as  insoluble  earthy  phosphates.  It 
is  also  abundant  in  guano,  the  excrement  of  seafowl. 

Phosphorus  is  now  always  extracted  from  calcic  phosphate, 
which  is  generally  obtained  from  bones. 

Exp.  172. — Burn  a  few  bones  in  the  open  fire.  They  will 
leave  more  than  half  their  weight  of  a  white  ash.  Grind  this  ash 
to  a  fine  powder,  and  mix  30  grams  of  it  with  20  grams  of  oil  of 
vitriol  and  180  or  200  grams  of  water.  After  standing  for  some 
hours,  strain  off  the  acid  liquor  from  the  calcic  sulphate  which  is 
formed.  Preserve  this  liquor  for  preparing  some  of  the  soluble 
phosphates. 


Properties  of  Phosphorus.  161 

The  change  in  this  experiment  consists  in  the  removal  of 
two-thirds  of  the  calcium  by  the  sulphuric  acid,  in  the  in- 
soluble form  of  calcic  sulphates ;  the  bone  earth,  which  is 
not  soluble  in  water,  becoming  converted  into  a  very  soluble 
acid  phosphate,  as  shown  by  the  equation — 

Tricalcic  Phosphate      Sulphuric  Acid  Acid  Phosphate  Calcic  Sulphate 

Ca32PO4  +  2H2SO4  =  CaH42PO4  +  2CaSO4 
If  phosphorus  is  to  be  made,  a  solution  of  the  acid  phos- 
phate, or  superphosphate  of  lime,  prepared  by  a  similar  process, 
is  evaporated  down  to  a  syrupy  consistence,  and  mixed  with 
about  a  third  of  its  weight  of  powdered  charcoal,  after  which 
it  is  heated  nearly  to  redness.  It  is  then  placed  in  an  earthen 
retort,  and  slowly  raised  to  a  full  red  heat.  Phosphorus 
gradually  comes  over  in  vapour,  and  is  condensed  in  water, 
while  a  large  quantity  of  hydrogen  and  carbonic  oxide  gases 
pass  off,  leaving  a  considerable  residue  of  bone  earth  in  the 
retort.  The  superphosphate  when  heated  with  charcoal  is 
decomposed.  Its  calcium  retains  sufficient  phosphorus  and 
oxygen  to  reconvert  it  into  tricalcic  phosphate,  3(CaH42PO4) 
becoming  Ca3,  2?O4  +  4H3PO4  ;  while  the  phosphoric  acid 
in  the  presence  of  the  charcoal  breaks  up  as  follows  : — 

4H3P04  +  i6C  =  P4  +  6H2  +  i6CO. 
The  phosphorus  is  purified  by  melting  it  under  warm 
water,  heating  it  with  chloride  of  lime,  and  forcing  it,  by 
pressure,  through  washleather;  it  is  then  moulded,  while 
in  the  fluid  state,  by  allowing  it  to  flow  into  tubes,  which  are 
next  chilled  in  cold  water,  and  the  phosphorus  becomes 
solid. 

Phosphorus  is  a  soft,  semi-transparent,  waxy-looking  sub- 
stance, which  fumes  in  the  air,  and  forms  white  vapours, 
smelling  something  like  garlic.  The  fumes  are  feebly  lumi- 
nous in  a  dark  room,  and  hence  its  name,  which  means  the 
'light-bearer.'  It  has  a  sp.  gr.  of  1-83,  and  melts  at  44°. 
It  is  extremely  inflammable,  and  takes  fire  just  above  its 
melting  point.  On  this  account  it  must  always  be  kept 
under  water,  and  should  not  be  handled  with  warm  fingers. 


1 62  Safety  Matches. 

Phosphorus  is  not  soluble  in  water,  but  it  is  slightly 
so  in  ether ;  it  is  more  soluble  in  benzol,  oil  of  turpentine, 
and  in  the  fixed  oils. 

Phosphorus  is  also  known  in  two  other  allotropic  forms, 
viz.  white  and  red.  White  phosphorus  is  slowly  produced 
upon  the  sticks  of  phosphorus  when  kept  under  water. 
The  red  form,  or  amorphous  phosphorus,  is  prepared  in 
large  quantities  by  heating  phosphorus  for  several  hours  to 
about  260°  C.  in  closed  vessels,  filled  with  nitrogen  or  with 
carbonic  anhydride.  The  melted  phosphorus  gradually 
becomes  solid,  opaque,  and  of  a  deep  red  colour,  and  its  sp. 
gr.  becomes  increased -to  2-14.  In  this  form  it  is  insoluble 
in  carbon  disulphide,  which  may  be  used  to  dissolve  out  the 
last  traces  of  the  common  form.  When  quite  free  from 
ordinary  phosphorus,  red  phosphorus  may  be  exposed  to  the 
air  without  danger.  It  may  be  heated  in  the  open  air  be- 
yond 200°  without  taking  fire ;  but  if  raised  to  about  288° 
it  is  changed  into  the  common  form,  and  bursts  into  a  blaze. 
When  heated  in  vessels  full  of  nitrogen,  it  may  be  distilled 
like  common  phosphorus,  the  vapour  condensing  in  clear, 
colourless  drops.* 

Exp.  173. — Dissolve  i  or  2  decigrams  of  phosphorus  in 
2  c.  c.  of  carbon  disulphide  in  a  test-tube;  pour  a  little  of  the 
solution  upon  a  piece  of  filtering-paper,  and  allow  it  to  dry.  The 
phosphorus  will  be  left  in  a  finely  divided  form,  and  will  set  fire 
to  the  paper  in  a  few  minutes. 

Red  phosphorus  is  employed  in  preparing  safety  matches. 
The  matches  are  covered  with  melted  parafrme,  and  tipped 
with  a  paste  consisting  of  potassic  chlorate,  antimoniou 
sulphide,  powdered  glass,  and  gum  water.     When  they  ar 
to  be  lighted,  they  are  rubbed  upon  a  surface  covered  with  ; 
mixture  of  red  phosphorus  with  half  its  weight  of  powdered 
glass.     Common  lucifer-matches  have  the  phosphorus  mixe 

*  The  vapour  of  phosphorus  has  twice  as  many  atoms  in  its  molecul( 
as  most  elements,  4  atoms  of  phosphorus  instead  of  2  being  containe 
in  the  molecule.  Arsenicum  resembles  phosphorus  in  this  respect. 


Oxides  of  Phosphorus.  163 

up  in  the  paste  with  which  they  are  tipped,  and  these  take  fire 
when  rubbed  on  any  rough  surface.  The  safety  matches 
can  only  be  kindled  by  friction  on  the  phosphorised  surface. 

Exp.  1 74. — Place  a  bit  of  phosphorus  in  a  solution  of  argentic 
nitrate.  In  the  course  of  a  day  or  two  it  will  be  covered  with 
brilliant  crystals  of  reduced  silver. 

Solutions  of  salts  of  copper,  platinum,  or  gold  will  also 
yield  up  their  metal  if  used  instead  of  solution  of  a  silver 
salt,  owing  to  the  strong  attraction  of  phosphorus  for  oxygen. 

Phosphorus  combines  with  many  of  the  metals  when 
heated  with  them.  Such  compounds  are  called  phosphides. 

(37)  Phosphorus  forms  two  well-marked  oxides — phos- 
phoric anhydride  (P2O5)  and  phosphorous  anhydride  (P2OS). 
They  give  powerful  acids  when  combined  with  water,  viz. 
phosphoric  acid  (H3PO4)  and  phosphorous  acid  (H2PHO3) ; 
besides  which,  there  is  a  third  acid,  the  hypophosphorous 
(HPH2O2),  with  still  less  oxygen. 

Phosphoric  Anhydride  (P2O5). 

Exp.  175.— Dry  two  or  three  pieces  of  phosphorus  of  the  size 
of  a  pea  upon  blotting-paper,  and  place  them  upon  a  small  cap- 
sule in  the  middle  of  a  plate.  Touch  the  phosphorus  with  a  hot 
wire,  and  cover  it  at  once  with  a  dry  gas  jar.  White  flakes  of 
the  anhydride  will  be  formed,  and  will  settle  down  upon  the 
plate. 

This  anhydride  is  a  snow-white  powder,  which  attracts 
moisture  quickly ;  it  hisses  when  a  few  drops  of  water  are 
added  to  it ;  it  dissolves  quickly,  except  a  few  flocculi,  and 
produces  phosphoric  acid,  which  is  intensely  sour,  but  not 
caustic — 

P205  +  3H20     =     2H3P04. 

It  is  easily  made  in  large  quantities  by  burning  dry  phos- 
phorus in  a  dish  hung  in  a  large  globe  supplied  with  a  current 
of  dry  air. 

Phosphoric  acid  may  be  formed  by  dissolving  phosphorus 
in  about  13  times  its  weight  of  diluted  nitric  acid  of  sp.  gr. 
i '20.  Concentrated  acid  must  not  be  used,  as  it  acts  with 

M    2 


164  Sodic  Phosphates. 

great  violence.  The  phosphorus  becomes  oxidized  by  the 
nitric  acid,  which  is  decomposed ;  and  on  boiling  down  the 
solution  the  excess  of  nitric  acid  is  driven  off,  and  pure 
phosphoric  acid  is  obtained  in  solution.  If  the  water  be 
driven  off  as  far  as  possible,  the  acid  is  left  in  a  form  which 
fuses  at  a  low  red  heat,  and  becomes  a  clear,  glassy-looking 
solid  on  cooling.  This  glass  dissolves  easily  in  water. 

Besides  ordinary  phosphoric  or  orthophosphoric  acid,  as  it 
is  termed,  (H3PO4),  two  other  distinct  acids  closely  related 
to  it  are  known,  viz.  metaphosphoric  acid  (HPO3) ;  and 
pyrophosphoric  acid  (H4P2O7)  j  each  of  these  forms  a  special 
set  of  salts. 

The  ordinary  phosphoric  acid  is  prepared  by  dissolving 
phosphorus  in  nitric  acid,  as  already  described.  If  the 
glassy  acid  thus  obtained  be  boiled  with  water,  and  made 
slightly  alkaline  with  sodic  carbonate,  a  salt  is  obtained,  the 
disodic  hydric  phosphate,  which  on  crystallisation  gives  efflo- 
rescent rhombic  prisms  (Na2HPO4,  i2H2O). 

Exp.  176. — Take  the  solution  of  superphosphate  of  lime  pre- 
pared as  directed  in  Exp.  1 72 ;  add  sodic  carbonate  until  the 
liquid  is  faintly  alkaline;  filter  it  from  the  precipitated  calcic 
phosphate,  and  evaporate  the  solution  till  a  drop  of  it  crystallises 
when  allowed  to  cool  on  a  slip  of  glass.  Then  allow  the  whole 
solution  to  cool.  Crystals  of  disodic  hydric  phosphate  will  be 
formed. 

If  this  disodic  hydric  phosphate,  or  rhombic  phosphate,  as  it 
is  sometimes  called,  be  mixed  with  an  excess  of  caustic  soda, 
a  crystallisable  salt,  formerly  called  subphosphate  of  soda, 
with  the  formula  Na3PO4,  i2H2O,  or  trisodic  phosphate, 
is  obtained.  If  a  quantity  of  phosphoric  acid  be  divided 
into  two  equal  parts,  one  of  which  is  just  neutralised  with 
sodic  carbonate,  and  then  the  other  half  of  the  acid  be 
added,  a  third  salt  is  obtained,  which  crystallises  with  diffi- 
culty. It  was  formerly  known  as  biphosphate  of  soda.  It 
is  the  dihydric  sodic  phosphate  (NaH2PO4,  H2O). 

Thus  it  is  possible  to  form  three  different  sodium  salts 


Sodic  Phosphates.  165 

from  the  common  phosphoric  acid,  in  which  the  hydrogen 

of  the  acid  is  displaced  step  by  step  : — 

Tribasic  phosphoric  aeid  H3PO4 

Dihydric  sodic  phosphate  NaHaPO4,  HaO 

Hydric  disodic  phosphate  NaaHPO4,  I2H^O 

Trisodic  phosphate  Na3PO4,  I2H*O 

These  salts  all  give  a  yellow  precipitate  with  argentic 
nitrate,  or  triargentic  phosphate  (Ag3PO4).  They  also  give, 
when  mixed  with  ammonia  and  magnesic  sulphate,  a  crystal- 
line precipitate  of  ammonic  magnesic  phosphate  (H4N, 
Mg"P04,  6H20). 

Exp.  177. — Dry  a  portion  of  the  disodic  hydric  phosphate 
crystals  at  1 50°  C.  They  will  lose  their  water  of  crystallisation, 
and  leave  a  white  mass* 

This  consists  of  Na2HPO4.     If  it  be  redissolved  in  water, 
it  will  furnish  the  original  salt,  known  by  its  property  of  pre- 
cipitating silver  nitrate  yellow — 
Na2HPO4  +  3AgNO3   =   Ag3PO4  +  2NaNO3  +  HNO3. 

As  a  triargentic  phosphate,  the  solution  will  contain  nitric 
acid,  and  will  redden  litmus. 

Exp.  178. — Take  a  portion  of  the  same  sodium  salt,  and  heat 
it  to  redness  in  a  porcelain  crucible  before  redissolving  it  in  water. 

The  result  will  now  be  different :  two  molecules  of  the 
salt  coalesce,  and  lose  a  molecule  of  water,  2Na2HPO4  be- 
coming Na4P2O7  +  H2O.  If  the  residue  be  redissolved 
in  water,  the  salt  may  be  crystallised  with  ioH2O. 

Exp.  179. — Add  a  portion  of  the  solution  to  one  of  argentic 
nitrate,  and  a  white  precipitate  will  be  formed,  Na4P3O7  + 
4AgNO3  becoming  Ag4P2O7  +  4NaNO3. 

This  white  salt  is  the  pyrophosphate,  so  called  because 
obtained  by  the  action  of  fire  upon  the  common  phosphate. 

Exp.  1 80. — Heat  a  little  of  the  dihydric  sodic  phosphate  to 
redness  :  it  becomes  converted  into  a  glassy  mass  of  sodic  meta- 
phosphate,  the  elements  of  water  being  expelled — 
NaHaPO4,  H,O     =     NaPO3   +   2HaO. 


1 66  Phosphorus  and  Hydrogen. 

This  salt  belongs  to  a  class  known  as  the  metaphosphates, 
which  are  recognised  by  precipitating  argentic  nitrate  white 
and  gelatinous,  and  redissolving  the  precipitate  if  an  excess 
of  the  phosphate  be  used. 

The  pyrophosphoric  and  the  metaphosphoric  acids  may 
even  be  obtained  in  solution  in  water  by  decomposing  the 
silver  or  lead  salts  of  their  acids  by  means  of  sulphuretted 
hydrogen.  For  instance — 

Argentic  Metaphosphate  Metaphosphoric  Acid 

2AgPO3      +     H,S         =       2HPO3     +     Ag2S; 

Argentic  Pyrophosphate  Pyrophosphoric  Acid 

Ag4PaO7     +     2H2S       =       H4P,O7     +     2Ag,S; 
the  silver  and  the  hydrogen  changing  places. 

The  ordinary  triargentic  phosphate  would  yield  the 
common  form  of  the  acid — 

2Ag3P04  +  3H2S     =     2H3P04  +  3Ag2S. 

Acids  which,  like  the  metaphosphoric,  contain  one  atom 
of  hydrogen,  capable  of  displacement  by  a  metal,  are  called 
monobasic  acids.  Those  in  which  there  are  three  atoms  of 
hydrogen  which  admit  of  displacement  by  hydrogen,  like  the 
ordinary  form  of  phosphoric  acid,  are  called  tribasic  acids  ; 
while  in  such  cases  as  the  pyrophosphoric,  which  contain 
four  atoms  of  displaceable  hydrogen,  the  acid  is  said  to  be 
tetrabasic. 

The  phosphorous  and  hypophosphorous  acids  are  of  little 
importance. 

(37  a)  With  hydrogen  phosphorus  forms  three  compounds : 
one  solid  (HP2) ;  one  liquid  (H10P5),  the  vapour  of  which 
inflames  immediately  on  reaching  the  air ;  and  a  gas  (H3P). 
This  is  the  only  hydride  of  phosphorus  that  we  shall  describe. 

PHOSPHURETTED  HYDROGEN  :  Symb.  H3P ;  Atom,  and 
MoL  Wt.  34;  Sp.  Gr.  1-185  ;  &&  Wt.  17. 

This  is  a  poisonous  gas,  with  a  disgusting  odour  of  garlic, 
highly  inflammable,  and  liquefiable  under  pressure.  It  is 
decomposed  by  chlorine,  and,  though  not  soluble  in  water, 


Phosphorus  and  Chlorine.  167 

is  wholly  absorbed  by  a  solution  of  bleaching-powder.     It 
-  precipitates   the  salts   of  lead  and  copper  black  (forming 
phosphides),  and  corrosive  sublimate  yellow. 

Exp.  181. — Dissolve  4  grams  of  caustic  potash  in  16  grams  of 
water;  place  it  in  a  small  retort  of  about  50  c.  c.  capacity,  and 
add  2  or  3  decigrams  of  phosphorus ;  immerse  the  beak  of  the 
retort  just  below  the  surface  of  water  in  a  small  capsule,  and 
heat  the  mixture  gently.  Bubbles  of  gas  will  form  in  the  retort, 
and  will  break  with  a  flash  and  a  slight  explosion  upon  the  sur- 
face of  the  potash  solution.  By  degrees  the  air  of  the  retort 
will  be  deprived  of  all  its  oxygen,  and  then  the  bubbles  of  gas, 
as  they  escape  into  the  air,  will  take  fire,  producing  a  white 
wreath  of  phosphoric  anhydride,  which  forms  a  number  of  ring- 
lets, revolving  in  vertical  planes  around  the  axis  of  the  wreath 
itself  as  it  ascends. 

In  this  beautiful  experiment,  which  requires  care,  lest  the 
retort  be  broken  by  the  bursting  of  the  bubbles  within  it, 
phosphuretted  hydrogen  gas  is  formed,  accompanied  by 
traces  of  the  vapour  of  the  liquid  phosphide,  which  causes  it 
to  take  fire  as  soon  as  it  mixes  with  the  air — 

Potash  Phosph.  Potass.  Hypo- 

Hydrogen  phosphite 

P4     +     3H,O     +     3KHO     =     H3P     +     3KPH2O3. 

Pure  phosphuretted  hydrogen,  which  does  not  take  fire 

spontaneously,  is  obtained  by  heating  phosphorous  acid,  which 

breaks  up  into  phosphoric  acid  and  phosphuretted  hydrogen — . 

4H2PHO3     =     3H3P04  +   H3P. 

Phosphuretted  hydrogen  is  feebly  alkaline  in  its  nature, 
which  is  in  some  measure  analogous  to  that  of  ammonia,  to 
which  it  corresponds  in  composition,  but  it  contains  only 
half  a  volume  of  phosphorus  vapour  and  three  volumes  of 
hydrogen  in  two  volumes  of  the  gas. 

Phosphorus  burns  when  placed  in  chlorine  gas.  When 
the  chlorine  is  in  excess,  it  forms  a  solid  volatile  chloride 
(PC15),  which,  when  put  into  water,  produces  phosphoric 
and  hydrochloric  acids — 

PC15  +  4H2O     «=     H3PO4  +   5HC1. 


1 68  Silicon. 

If  the  phosphorus  is  in  excess,  a  liquid  chloride  (PC13)  is 
formed;  and  this  furnishes  with  water  phosphorous  and 
hydrochloric  acids — 

PC13  +  3H20     -     H2PH03  +  3HC1. 
There  are  corresponding  bromides  of  phosphorus. 


CHAPTER  IX. 

SILICON   AND    BORON. 

(38)  Silicon,  in  combination  with  oxygen  as  silica  or 
silex,  is  the  most  abundant  solid  material  found  upon  the 
earth.  It  forms  the  essential  substance  of  flint,  sea  sand, 
sandstone,  quartz,  agate,  and  calcedony,  besides  entering 
largely  into  the  composition  of  clay,  and  a  great  number  of 
crystallised  minerals,  and  nearly  all  the  common  rocks, 
except  limestone. 

SILICON — Symb.  Si;  Atom.  Wt.  28;  Sp.  Gr.  2*49 — is  never 
found  uncombined,  but  is  always  obtained  by  chemical 
means,  one  method  being  the  heating  of  sodium  in  the 
vapour  of  silicic  chloride  (SiCl4),  when  common  salt  is 
formed  and  silicon  is  set  free.  It  is  a  brown  powder,  which 
burns  when  heated  strongly  in  air  or  oxygen,  but  which  at  a 
very  high  heat,  though  below  that  required  for  fusing  steel, 
may  be  melted  if  excluded  from  air.  It  may  be  obtained 
crystallised  in  plates  and  octahedra,  which  are  hard  enough 
to  scratch  glass. 

Silicon  forms  only  one  oxide,  viz.  silica  (SiO2),  and  this  is 
found  both  crystallised  and  amorphous.  Pure  crystalline 
silica  has  a  sp.  gr.  of  2*642.  It  occurs  in  quartz  in  six-sided 
prisms,  ending  in  six-sided  pyramids.  Amethyst  is  a  purple 
variety  of  quartz.  The  amorphous  form  of  silica  has  a  sp. 
gr.  of  only  2*2  ;  it  may  be  obtained  by  melting  quartz 
before  the  oxyhydrogen  blowpipe.  Calcedony  is  a  mechanical 


Silica.  169 

mixture  of  crystalline  and  amorphous  quartz.  Agate  consists 
of  a  succession  of  layers  of  crystalline  and  amorphous  silica. 
Flint  is  a  form  of  calcedony  chiefly  found  in  the  upper  chalk  ; 
and  opal  is  a  hydrated  variety  of  amorphous  silica. 

Silica,  when  once  crystallised,  is  insoluble  in  water,  and 
in  all  acids  except  the  hydrofluoric. 

Silica,  in  fine  powder,  looks  like  a  white  earth,  but  it  has 
a  strong  tendency  to  unite  with  bases,  a  property  which  may 
be  employed  to  obtain  it  in  a  pure  form. 

Exp.  182.— Place  about  60  grams  of  a  mixture  of  potassic 
und  sodic  carbonates  in  a  clay  crucible,  and  raise  it  to  a  red 
heat;  when  fused  add  15  grams  of  ground  flint  or  of  fine  sand  to 
the  melted  mass :  effervescence  is  produced  slowly,  due  to  the 
escape  of  carbonic  anhydride,  and  the  silica  is  gradually  dis- 
solved. When  the  decomposition  is  over,  pour  out  the  mass  on 
a  stone  slab,  and  after  it  has  cooled  let  it  digest  in  water :  most 
of  it  will  dissolve,  with  the  exception  of  some  impurities,  such  as 
oxide  of  iron. 

The  solution  thus  obtained  consists  of  a  mixture  of  sili- 
cates of  potash  and  soda,  with  a  large  excess  of  the  alkalies. 

A  smaller  proportion  of  alkali  might  have  been  used,  but 
it  would  have  required  a  stronger  heat  to  melt  the  silicate, 
and  the  product  would  have  been  less  easily  soluble. 

Exp.  183. — Add  gradually  to  a  portion  of  this  solution  dilute 
hydrochloric  acid  in  excess :  the  mass  becomes  partly  or  wholly 
redissolved,  but  on  evaporating  it  the  silica  separates  at  first 
as  a  jelly-like  hydrate,  and  this,  by  further  drying,  becomes  con- 
verted into  a  white  earthy-looking  powder,  no  longer  soluble  in 
acids.  Wash  the  dry  mass  with  water  as  long  as  anything  is 
dissolved;  the  soluble  chlorides  may  thus  readily  be  removed, 
leaving  silica  in  a  nearly  pure  state,  in  the  amorphous  form. 

Exp.  184. — Heat  some  common  flints  to  redness  in  the  fire, 
and  suddenly  quench  them  in  water  :  they  become  very  friable, 
and  are  easily  reduced  to  a  fine  powder.  Heat  this,  add  hydro- 
chloric acid,  and  wash  thoroughly,  and  the  result  is  nearly  pure 
silica. 

Exp.  185. — To  another  portion  of  the  solution  of  silica  in  the 
alkalies  add  hydrochloric  acid  in  excess,  so  as  to  redissolve  the 


170  The  Silicates. 

whole.  Place  the  clear  solution  in  a  shallow  tray  formed  by 
tying  a  piece  of  parchment  paper  over  a  hoop  of  wood  or  of 
gutta  percha,  10  or  12  cm.  in  diameter,  and  float  this  little 
vessel  in  a  dish  of  water.  The  acid  and  saline  substances  are 
separated  by  dialysis  from  the  silica,  and  pass  out  into  the 
water.  If  the  water  in  the  dish  be  changed  twice  a  day,  the 
liquid  left  in  the  hoop  will,  in  three  or  four  days'  time,  be  found 
to  consist  of  a  solution  of  pure  silica  in  water,  and  may  be 
further  concentrated  by  cautious  evaporation. 

In  this  experiment  the  parchment  paper,  or  dialyser,  retains 
the  colloid,  or  gelatinous  form  of  silica,  while  it  allows  the 
crystalline  and  acid  particles  to  pass  through  its  pores  into 
the  water  on  the  other  side. 

The  solution  of  silica  is  tasteless,  limpid,  and  colourless ; 
but  if  the  evaporation  be  carried  too  far,  the  silica  separates 
in  the  form  of  a  jelly. 

Finely  divided  silica  may  be  gradually  dissolved  by  boil- 
ing it  with  the  alkalies  or  their  carbonates,  and  even  flints  in 
their  unground.  condition  may  be  dissolved  in  strong  solu- 
tions of  caustic  alkali  if  the  solution  be  digested  upon 
them  under  pressure.  The  Geysers,  or  hot  springs  of  Ice- 
land, contain  large  quantities  of  silica  dissolved,  and  as  the 
liquid  cools  deposit  a  considerable  portion  upon  objects 
exposed  in  the  stream.  They  are  then  often  said  to  be 
'  petrified/  or  converted  into  stone,  the  silica  being  deposited 
in  the  interstices,  and  preserving  the  appearance  of  the 
original  structure. 

(39)  Silicates:  Glass. — The  silicates  are  very  abundant 
natural  productions.  Silica  combines  with  bases  in  several 
different  proportions,  and  forms  a  great  variety  of  crystal- 
lised minerals,  many  of  which  are  double  silicates  of  complex 
nature. 

Glass  consists  of  a  mixture  of  several  silicates,  which,  when 
heated  to  a  particular  temperature,  are  plastic  and  viscous, 
and  retain  their  transparency  on  cooling.  The  nature  and 
proportions  of  the  silicates  present  are  made  to  vary  accord- 
ing to  the  use  to  which  the  glass  is  to  be  applied.  The  degree 


Varieties  of  Glass.  171 

of  fusibility  of  the  silicates  varies  widely.  Fire-clay,  or  alumina 
silicate  (A12O3,  2SiO2),  is  nearly  infusible  in  the  furnace, 
and  it  is  the  material  of  which  fire-bricks  and  crucibles  are 
made.  Calcic  silicate  is  also  very  infusible,  whereas  the 
ferrous  silicate  (FeO,  2SiO2)  constitutes  the  *  bull-dog'  or 
fusible  slag,  of  iron  refiners.  Lead  silicate  (aPbO,  3SiO2)  is 
still  more  fusible,  and  furnishes  a  clear  yellowish  glass.  The 
silicates  of  potash  and  soda  are  also  very  fusible.  All  these 
silicates,  when  mixed  with  each  other,  melt  at  much  lower 
temperatures  than  they  do  when  separate.  Many  of  them, 
when  thus  melted,  possess  the  exceptional  property  of 
viscosity,  between  the  point  of  perfect  liquidity  and  solidifi- 
cation. It  is  this  viscous  condition  which  enables  glass  to 
be  moulded  into  the  countless  forms  required  for  art  or 
luxury.  Good  glass  also  has  the  valuable  property  of  not 
crystallising  as  it  cools ;  in  certain  cases  some  of  the  silicates, 
however,  do  crystallise  out,  and  then  the  glass  becomes 
opaque,  and  though  the  separate  silicates  of  which  it  con- 
sists are  more  or  less  readily  attacked  by  water  and  acids,  if 
the  proportions  of  the  mixture  are  properly  selected,  glass 
formed  from  these  silicates  is  no  longer  soluble.  The 
different  varieties  of  glass  are  not  to  be  regarded  as  definite 
compounds,  but  as  mixtures  in  varying  proportions  of  their 
component  silicates,  which,  however,  in  the  best  kinds 
generally  approach  some  simple  atomic  proportions. 

Much  care  is  requisite  in  selecting  the  materials  for  the 
finer  kinds  of  glass.  Potash  is  preferred  to  soda,  because 
the  glass  made  from  soda  has  a  bluish  green  tinge.  Soda 
gives  a  more  fusible  glass.  The  addition  of  lime  increases 
its  hardness  and  lustre,  but  diminishes  its  fusibility.  An 
excess  of  lime  is  apt  to  make  it  milky-looking. 

i.  Window  glass,  or  crown  glass,  is  made  of  a  mixture  of 
silicates  of  soda  and  lime.  100  parts  of  pure  white  sand,  35  or 
40  of  chalk,  30  of  soda  ash,  and  from  50  to  150  of  broken  glass, 
or  cutlet,  are  the  proportions  often  used.  The  mixture  is 
heated  gradually,  to  prevent  it  from  frothing  up,  and  is  after- 


I?  2  Properties  of  Glass. 

wards  raised  to  a  very  intense  heat.  Plate  glass  contains  the 
same  materials  in  different  proportions.  2.  Bottle  glass 
contains  a  smaller  proportion  of  silica  than  either  window  or 
plate  glass,  and  is  made  of  much  coarser  materials.  It  con- 
sists of  a  mixture  of  silicates  of  soda,  lime,  alumina,  and 
iron.  3.  Bohemian  glass,  which  is  very  hard  and  infusible, 
is  a  mixture  of  silicates  of  potash  and  lime.  It  is  used  for 
making  the  combustion  tubes  employed  in  the  analysis  of  or- 
ganic substances,  and  hence  is  much  prized  in  the  laboratory. 
4.  The  ordinary  white,  m  flint  glass,  consists  almost  entirely 
of  silicates  of  potassium  and  lead.  The  proportions  of  ma- 
terials used  are — 300  of  fine  sand,  200  of  red  lead,  100  of 
refined  pearlash,  and  about  30  parts  of  nitre.  The  oxide  of 
lead  renders  the  glass  much  heavier  and  more  fusible,  giving 
it  a  higher  refractive  and  dispersive  power  upon  light,  and 
greater  brilliancy,  but  it  makes  it  softer  and  more  easily 
tarnished,  and  it  is  also  liable  to  be  corroded  by  alkaline 
solutions. 

Glass,  when  melted,  dissolves  many  of  the  metallic  oxides 
without  losing  its  transparency,  but  becomes  coloured  with 
tints  varying  according  to  the  metallic  oxide  employed. 
Cobalt  gives  a  splendid  sapphire  blue,, manganese  a  violet, 
uranium  a  yellow,  ferrous  oxide  a  green,  ferric  oxide  a 
yellow  or  reddish-brown,  cupric  oxide  a  green,  and  cupreous 
oxide  a  ruby-red. 

Well-made  glass  is  not  acted  on  by  any  acid  or  mixture 
of  acids,  except  the  hydrofluoric,  which  last  removes  its 
silica ;  but  it  is  not  quite  insoluble.  If  left  long  in  water, 
or  buried  in  moist  earth,  it  becomes  slowly  decomposed. 
This  is  often  seen  in  wine-bottles,  which  exhibit  the  brilliant 
colours  of  thin  plates,  due  to  the  scaling  off  from  the  surface 
of  flakes  detached  by  slow  chemical  action  of  moisture. 

Exp.  1 86. — Grind  a  little  glass  to  a  fine  powder  in  a  mortar ; 
place  it  on  a  piece  of  moistened  turmeric  paper  :  sufficient 
alkali  will  be  dissolved  by  the  water  to  tinge  the  turmeric 
brown, 


Compounds  of  Silicon.  173 

If  glass  articles  are  allowed  to  cool  rapidly  by  exposing 
them  while  red  hot  to  the  air,  they  become  inconveniently 
brittle.  The  outer  surface  becomes  solid,  whilst  the  inner 
portion  remains  dilated  by  the  heat :  as  the  mass  cools,  the 
particles  within,  by  their  adhesion  to  the  external  solid  por- 
tion, are  still  held  in  their  dilated  state.  A  very  slight  force, 
such  as  a  scratch  on  the  surface,  or  the  change  of  tem- 
perature from  a  cold  room  to  a  warm  one,  will  often  cause 
them  to  crack.  In  order  to  avoid  this  inconvenience,  the 
glass  is  annealed,  or  placed  in  a  chamber  heated  nearly  to 
redness,  where  the  material  is  allowed  to  cool  very  slowly, 
by  which  means  the  particles  are  enabled  to  assume  their 
natural  position  with  regard  to  each  other. 

Glass,  however,  is  a  bad  conductor  of  heat,  but  dilates 
considerably  when  heated,  so  that  even  after  annealing  it  is 
liable  to  crack  when  exposed  to  sudden  changes  of  tem- 
perature, such  as  that  produced  by  pouring  boiling  water  into 
a  cold  glass,  especially  if  it  be  thick. 

Exp.  187. — Take  one  of  the  drops  of  glass  formed  by  allow- 
ing melted  glass  to  fall  into  water,  and  suddenly  nip  off  the 
tail :  the  glass  flies  to  pieces  with  a  kind  of  explosion,  and  is 
reduced  almost  to  powder. 

Exp.  1 88. — Grind  3  or  4  grams  of  fluor  spar  to  fine  powder, 
and  mix  it  with  an  equal  weight  of  powdered  glass  or  fine  sand. 
Introduce  it  into  a  Florence  flask  previously  fitted  with  a  sound 
cork  and  a  tube  bent  downwards  for  delivering  gas.  Pour  upon 
the  mixture  about  30  grams  of  oil  of  vitriol,  insert  the  cork  and 
tube,  and  apply  a  gentle  heat :  a  densely  fuming  gas  is  dis- 
engaged, consisting  of  silicic  fluoride. 

The  change  that  takes  place  may  be  thus  represented — 
2CaF2  +  2H2SO4  +  SiO2    =    SiF4  +  2CaSO4  4-  2H2O. 

The  gas  (SiF4)  must  not  be  inhaled,  as  it  is  very  irritating, 
and  produces  coughing.  When  dry,  it  is  colourless  and 
transparent.  Water  produces  a  remarkable  change  in  it. 

Exp.  189.— Pass  the  gas  into  a  glass  of  water.  Each  bubble 
as  it  rises  becomes  coated  with  a  white  opaque  film,  composed  of 


1/4  Boron. 

hydrated  silica,  while  the  liquid  becomes  intensely  acid,  from  the 
formation  of  a  new  acid  (the  hydrofluosilicic),  water  being  de- 
composed at  the  same  time — 

3SiF4   +   2H,O   =   SiOa   +   2(2HF,  SiFj. 

It  is  owing  to  the  strong  tendency  to  the  formation  of 
silicic  fluoride  that  hydrofluoric  acid  corrodes  glass  so 
rapidly. 

Silicon  also  forms  a  compound  with  chlorine  (SiCl4),  and 
with  bromine  (SiBr4),  both  of  which  are  volatile  liquids 
which  are  decomposed  by  water.  A  remarkable  gaseous 
compound  with  hydrogen  (SiH4)  is  also  known.  It  takes 
fire  as  soon  as  it  escapes  into  the  air,  and  may  be  procured, 
mixed  with  hydrogen,  by  decomposing  a  compound  of 
silicon  and  magnesium  by  means  of  hydrochloric  acid. 

Silicon  belongs  to  the  group  of  tetrad  elements :  it  has 
certain  points  of  resemblance  with  the  rare  substances 
titanium  and  zirconium  on  the  one  hand,  and  with  carbon 
on  the  other.  All  these  elements  form  volatile  compounds 
with  four  atoms  of  chlorine  (CC14,  SiCl4,  TiCl4,  ZrCl4) 
These  chlorides  are  colourless  liquids,  except  zirconic 
chloride,  which  is  solid. 

(390)  BORON:  Symb.-!&;  Atom.  Wt.  n. 

This  is  the  characteristic  element  in  bcracic  acid,  which 
enters  into  the  formation  of  borax,  the  sodium  salt  of  this 
acid.  It  is  an  olive-brown  powder,  which  may  be  obtained 
by  fusing  5  parts  of  boracic  acid  with  3  of  sodium  in  a 
covered  iron  crucible,  previously  made  red  hot,  covering  the 
mixture  with  three  parts  of  common  salt,  previously  fused, 
and  broken  into  coarse  powder.  .An  intense  action  occurs, 
and  the  mass  becomes  melted.  It  is  to  be  poured  in  this 
red-hot  condition  into  a  large  and  deep  vessel  containing 
water  acidulated  with  hydrochloric  acid.  The  boron  re- 
mains undissolved.  By  fusing  it  with  aluminum,  in  which 
metal  it  is  dissolved,  boron  has  also  been  obtained  in 
crystals,  which  are  transparent,  and  nearly  as  hard  as 


Properties  of  Borax.  175 

diamond.  This  element  is  remarkable  for  its  power  of 
combining  directly  with  nitrogen  when  heated  in  the  gas, 
forming  a  grey  powder.  When  heated  with  chlorine  it 
burns  freely,  and  combines  with  it,  furnishing  a  gas  (BC13), 
which  is  immediately  decomposed  by  water  into  boracic  and 
hydrochloric  acids — 

2BC13  +  4H2O     =     6HC1  +   2HBO2. 

Boracic  Anhydride  (Symb.  B2O3)  is  the  only  known  oxide 
of  boron.  It  combines  with  water,  and  then  forms  boracic 
acid,  which  crystallises  in  white,  pearly-looking  scales 
(HBO2,  H20)  ;  for— 

B203  +   3H20     =     2(HBO2H2O). 

The  most  abundant  source  of  boracic  acid  is  the  district 
called  the  Maremma,  in  Tuscany,  where  it  occurs  in  the  un- 
combined  state.  It  issues  in  small  quantities  in  the  jets  of 
steam  called  soffioni,  which  are  produced  by  volcanic  heat. 
These  jets  are  directed  into  basins  formed  of  brickwork  and 
filled  with  water,  when  the  steam  is  condensed,  and  a  weak 
solution  of  boracic  acid  obtained.  This  solution  is  con 
centrated  in  shallow  pans  by  the  heat  of  the  jets  of  steam 
themselves,  directed  beneath  them,  and  the  acid  is  finally 
crystallised  out  on  cooling. 

Borax  (Na2O,  2B2O3,  ioH2O)  is  the  most  important  salt 
of  the  acid.  It  is  a  natural  production  obtained  by  the  ' 
drying  up  of  certain  lakes  of  Thibet,  and  it  has  lately  been 
found  in  California  and  in  some  other  localities.  The  crude 
Indian  borax  is  called  tincaL  Borax  is  used  as  a  flux  in 
soldering,  as  it  dissolves  most  metallic  oxides  and  leaves  a 
clean  surface  of  the  metal :  it  is  often  added  to  enamels,  for 
the  purpose  of  rendering  them  more  fusible,  and  is  used  by 
the  refiner  in  melting  gold  and  silver,  for  making  his  cru- 
cibles less  porous,  and  for  rendering  the  collection  of  the 
metal  more  easy. 

Exp.  190. — Bend  the  end  of  a  piece  of  thin  platinum  wire,  8 
or  10  cm.  long,  into  a  small  hook;  heat  the  wire  to  redness,  and 


176  Boracic  Acid. 

instantly  touch  a  crystal  of  borax  as  large  as  a  split  pea  with  the 
wire  :  it  will  adhere  to  the  wire.  Then  introduce  the  wire  and 
crystal  into  the  flame  of  a  spirit  lamp.  The  borax  will  swell 
up,  become  opaque  and  white,  and  will  then  melt  into  a  clear 
glassy  bead. 

Borax  dissolves  many  metallic  oxides  when  melted  with 
them,  and  hence  is  often  used  as  a  test  before  the  blow- 
pipe (Fig.  66). 

Exp.  191. — Touch  the  bead  just  made  with  a  wire  moistened 
with  a  solution  of  cobalt  nitrate.  Then  melt  the  borax  again 
in  the  flame.  A  beautiful  blue  bead  is  obtained,  which  is 
almost  opaque  if  the  quantity  of  cobalt  be  considerable.  If  a 
scarcely  visible  fragment  of  manganese  oxide  be  used,  a  purplish 
bead  is  obtained. 

Boracic  acid  is  easily  obtained  from  borax. 

Exp.  192. — Dissolve  40  grams  of  borax  in  about  4  times  its 
weight  of  boiling  water;  add  to  the  hot  solution  10  grams  of 
oil  of  vitriol,  previously  mixed  with  its  own  bulk  of  water.  Sodic 
sulphate  is  formed,  and  remains  in  solution,  while  pearly  crystals 
of  boracic  acid  are  deposited  as  the  liquid  cools.  Pour  off  the 
solution,  dry  the  crystals  by  pressure  between  pieces  of  blotting- 
paper.  Place  a  few  of  them  on  a  slip  of  platinum  foil,  and  heat 
them  in  the  flame  of  a  spirit  lamp.  Water  is  driven  off,  and  the 
anhydride  which  is  left  melts  into  a  clear  glass. 

Exp.  193. — Dissolve  a  few  crystals  of  the  boracic  acid  in  a 
small  dish  with  a  teaspoonful  of  alcohol.  Set  fire  to  the  spirit: 
it  burns  with  a  green  flame,  which  is  a  good  test  for  boracic 
acid.  A  similar  green  flame  is  obtained  if  a  crystal  of  borax  be 
moistened  with  sulphuric  acid  and  alcohol  added,  and  kindled 
as  before. 

This  green  flame,  when  seen  in  the  spectroscope,  contains 
a  series  of  peculiar  green  bands. 

Boron  forms  with  fluorine  a  gaseous  trifluoride  (BF13), 
which  is  easily  obtained  by  heating  boracic  anhydride  with 
twice  its  weight  of  powdered  fluor  spar  to  redness  in  an 
iron  tube. 

Boron  belongs  to  the  class  of  triad  elements,  but  in  many 
properties  it  resembles  silicon  more  than  any  other  element, 


177 


CHAPTER  X. 

COAL   GAS,    AND    OTHER   COMPOUNDS    OF    CARBON. 

(40)  The  two  elements  carbon  and  hydrogen  furnish  by 
their  union  a  very  numerous  series  of  compounds,  of  which 
some  are  gaseous,  some  liquid,  and  some  solid.  They  have 
received  the  general  name  of  hydrocarbons ;  but  the  full 
study  of  these  remarkable  substances  belongs  to  the  division 
of  chemical  science  known  as  organic  chemistry,  since  they 
are,  practically,  always  derived  from  the  decomposition  of 
bodies  of  organic  origin. 

Many  of  these  bodies  consist  of  absolutely  identical  pro- 
portions of  the  two  elements,  though  they  differ  widely  in 
properties.  When  compared  together  in  their  gaseous  state 
they  differ  in  density,  so  that  the  number  of  atoms  of  the 
elements  in  the  molecule  of  these  compounds  must  be 
different,  although  on  analysis  they  yield  the  same  propor- 
tions of  each  element.  Let  us  take,  for  instance,  a  few  of  the 
many  compounds  of  which  100  parts  consist,  of  8571  of 
carbon  and  14*29  of  hydrogen  : 

11*19  litres  of  olefiant  gas      (CaH4)  weigh  14  grams 
„  oil  gas  (C4H8)      „      28      „ 

„  octylenegas    (C8HI6)     „      56      „ 

„  cetylenegas    (Cl6H32)    ,,112      „ 

The  density  of  oil  gas  is  double  that  of  olefiant  gas  ;  whilst 
that  of  octylene  is  double  that  of  oil  gas,  and  cetylene  is 
double  that  of  octylene.  Such  bodies  are  said  to  be 
polymeric. 

OLEFIANT  GAS  (or  Ethylene) :  Symb.  C2H4 ;  Atom,  and 
Mol.  Wt.  28;  Sp.  Gr.  0-978;  Rel.  Wt.  14. 

Exp.  194. — Introduce  into  a  retort  which  will  hold  a  litre  30 
c.  c.  of  alcohol  and  60  c.  c.  of  oil  of  vitriol.  Heat  the  mixture,  and 
collect  the  gas  over  water ;  continuing  the  experiment  until  the 
mass  blackens  and  swells  up  considerably.  The  gas  consists  at 
first  chiefly  of  olefiant  gas,  mixed  with  ether  vapour;  but  towards 
the  end  it  becomes  mingled  with  sulphurous  anhydride 


178  Olefiant  Gas. 

The  production  of  olefiant  gas  is  due  to  the  removal  of 
the  elements  of  water  from  the  alcohol  by  the  action  of  the 
acid.  This  occurs  in  two  stages ;  in  the  first  of  which 
ethylsulphuric  acid  is  formed,  and  in  the  second  stage  this 
body  is  decomposed — 

Alcohol  Sulph.  Acid  Ethylsulph.  Acid  Water 

(1)  CaH6O     +     H2SO4      =       HCZH5S04     +     HaO 
And  ethylsulphuric  acid,  when  heated,  is  decomposed — 

(2)  HCZH5SO4 

becoming  olefiant  gas  (C2H4)  and  sulphuric  acid  (H2SO4). 

Olefiant  gas  has  no  colour,  but  a  faint  sweetish  smell,  as  of 
garlic.  It  is  but  little  soluble  in  water.  Under  great  pres- 
sures it  may  be  liquefied,  but  has  not  been  frozen.  It  is 
combustible,  but  will  not  support  life. 

Exp.  195. — Plunge  a  lighted  taper  into  a  small  jar  of  the  gas. 
The  taper  will  be  extinguished,  but  the  gas  will  burn  at  the 
mouth  of  the  jar  with  a  bright  smoky  flame. 

If  mixed  with  three  times  its  bulk  of  oxygen,  it  explodes 
violently  by  the  action  of  flame  or  of  the  electric  spark.  If 
care  be  taken,  the  gas  may  be  analysed  by  this  means  :  steam 
is  formed  and  immediately  condensed,  the  4  volumes  of  the 
mixture  giving  2  volumes  of  carbonic  anhydride — 
C2H4  +  3O2  =  2CO2  -h  2H2O. 

Exp.  196. — Mix  half  a  litre  of  the  gas  with  the  same  quantity 
of  chlorine,  and  let  the  mixture  stand  over  water:  the  two  gases 
combine  slowly  and  form  drops  of  a  yellowish  liquid,  which  col- 
lect on  the  surface  of  the  water,  and  sink  to  the  bottom  as 
they  increase  in  size. 

The  name  olefiant,  or  '  oil-maker/  gas  was  derived  from 
this  circumstance,  and  the  liquid  itself,  which  was  discovered 
by  some  Dutch  chemists,  is  called  Dutch  liquid  (C2H4C12). 

hxp.  197. — Mix  half  a  litre  of  olefiant  gas  in  a  tall  jar  with  a 
litre  of  chlorine,  and,  having  closed  the  jar  with  a  glass  plate, 
mix  the  gases  by  agitation;  then  apply  a  light.  The  mixture 
will  burn  quietly,  with  the  formation  of  a  dense  black  smoke. 


Marsh  Gas.  179 

The  chlorine  in  this  case  combines  with  the  hydrogen, 
forming  hydrochloric  acid,  while  the  whole  of  the  carbon  is 

separated  — 

C2H4  +   2C12     =     4HC1  +   C2. 

defiant  gas  is  one  of  the  substances  found  in  coal  gas, 
and  is  among  the  gases  given  off  when  fats  and  rosin  are 
decomposed  by  heat. 


MARSH  GAS:  Symb.  CH4—  ^  Methyl  Hydride  ((^.^  H)  — 
Atom.  andMol.  Wt.  16;  Sp.  Gr.  0-55;  Rel.  Wt.  8. 

This  is  the  simplest  of  the  compounds  of  carbon  with 
hydrogen.  It  is  easily  obtained,  in  an  impure  state,  mixed 
with  nitrogen  and  carbonic  anhydride,  by  stirring  the  mud 
of  stagnant  pools,  when  it  rises  in  bubbles  to  the  surface,  as 
a  result  of  the  decomposition  of  vegetable  matter.  It  is  also 
abundant  in  coal  gas,  as  it  is  one  of  the  substances  most 
frequently  produced  by  the  distillation  of  organic  matters  at 
a  high  temperature.  It  is  this  gas  which  escapes  from  the 
seams  of  coal,  and  which,  when  mixed  with  air,  fill's  the 
workings  of  the  mines  with  the  inflammable  material  known 
as  fire-damp,  and  this  gives  rise  to  the  disastrous  explosions 
which  occur  from  time  to  time  in  our  collieries. 

Marsh  gas  may  be  obtained  pure  by  distilling  one  of  the 
acetates  with  a  hydrated  alkaline  base  ;  for  example  : 

Sodic  Acetate  Sodic  Hydrate  Sodic  Carb.  Marsh  Gas 

NaCaH3Qa     +     NaHO       =       Na2CO3     +     CH4. 
Half  the  carbon  remains   behind  as  carbonate,  with  the 
whole  of  the  oxygen  in  combination  with  the  base;  while 
the  other  half  of  the  carbon  unites  with  the  whole  of  the 
hydrogen  to  form  marsh  gas. 

Marsh  gas  has  neither  colour,  odour,  nor  taste.  It  does 
not  support  life,  but  is  not  poisonous  if  breathed  when 
mixed  with  air.  It  is  but  very  slightly  soluble  in  water,  and 
has  not  been  liquefied  either  by  cold  or  pressure.  It  burns 
with  a  yellowish  flame.  It  requires  twice  its  bulk  of  oxygen 
for  complete  combustion,  and  then  explodes  with  the  forma- 

N   2 


180  The  Safety  Lamp. 

tion  of  its  own  bulk  of  carbonic  anhydride,  the  steam  which  is 
formed  becoming  immediately  condensed,  the  three  volumes 
of  gas  before  combustion  becoming  one  afterwards — 
CH4  +   2O2     =     CO2  +   2H2O. 

If  a  mixture  of  about  10  volumes  of  air  with  i  of  marsh 
gas  be  made,  it  will  contain  the  quantity  of  oxygen  necessary 
for  complete  combustion,  and  will  explode  powerfully  on 
the  approach  of  a  light ;  8  volumes  of  nitrogen  and  i  of 
carbonic  anhydride  will  be  produced,  while  the  steam  will 
be  immediately  condensed.  Hence  the  after- damp,  or  air 
left  in  a  mine  after  an  explosion  has  occurred,  is  entirely 
unfit  for  the  support  of  human  life ;  so  that  persons  exposed 
to  its  influence  perish  as  surely  as  they  do  from  the  direct 
effects  of  the  flame. 

Marsh  gas,  mixed  with  iess  than  between  two  and  three 
times  its  bulk  of  air,  does  not  explode  on  the  application  of 
flame  ;  and,  if  diluted  with  more  than  1 8  or  20  parts  of  air,  it 
only  burns  rapidly,  but  does  not  explode  with  sudden  violence 

Sir  H.  Davy's  safety  lamp  was  contrived  for  the  purpose 
of  preventing  these  calamitous  explosions  in  mines.  Ma 
gas  requires  a  high  temperature  to  set  it  on  fire  ;  so  that,  to 
kindle  it,  a  substance  must  be  not  merely  red  hot,  but  nearly 
white  hot. 

Exp.  198. — Twist  a  piece  of  rather  thick  platinum  wire  5  or  (. 
times  round  a  thin  glass  rod,  so  as  to  form  a  coil  at  one  end 
the  wire ;  hold  this  coil  in  the  flame  of  a  spirit  lamp  until  it  is  re 
hot,  then  instantly  place  it  in  a  jet  of  coal  gas  which  is  not  bur 
ing,  but  is  allowed  to  escape  into  the  air.  The  wire  will  continue 
to  glow  without  kindling  the  gas. 

Exp.  199. — Place  a  sheet  of  iron  or  copper  wire  gauze,  con- 
taining about  ico  meshes  in  a  square  centimetre,  over  the  flame 
of  a  spirit  lamp  :  the  flame  will  not  pass  through  the  gauze,  owing 
to  its  being  cooled  down  below  its  inflaming  point.  A  piece  < 
coarse  gauze  containing  from  4  to  9  meshes  in  the  sq.  centin 
will  not  prevent  the  flame  from  passing  through. 

Sir  H.  Davy's  safety  lamp  is  merely  an  oil  lamp,  enclosed 


Nature  of  Flame.  1 8 1 

within  a  cylinder  of  fine  wire  gauze  provided  with  a  double 
top,  and  with  a  crooked  wire  passing  up  through  the  body 
of  the  lamp  to  trim  the  wick.  When  such  a  lamp  is  intro- 
duced into  an  atmosphere  containing  fire-damp,  the  flame  is 
seen  to  enlarge  until,  when  the  proportion  of  marsh  gas 
becomes  large,  it  burns  on  the  inner  surface  of  the  cylinder. 
Whenever  this  pale  enlarged  flame  is  seen,  the  miner  must 
withdraw;  for  though  no  explosion  can  occur  while  the 
gauze  is  sound,  yet  the  metal  at  that  high  temperature 
becomes  corroded,  and  might  easily  break  into  holes,  and  a 
single  large  hole  would  be  sufficient  to  cause  an  explosion. 

Flame  is  never  produced  by  a  burning  body,  unless  that 
body  is  converted  into  vapour  before  it  burns ;  charcoal  and 
iron,  for  instance,  are  not  volatile,  and  they  do  not  burn 
with  flame ;  but  phosphorus,  sulphur,  and  zinc,  all  of  which 
are  volatilised  before  they  take  fire,  burn  with  flame.  Flame 
is  hollow,  and  contains  unburned  combustible  matter  within, 
forming  in  fact  a  sort  of  luminous  bubble. 

Exp.  200. — Support  one  end  of  a  glass  tube,  12  or  14.  cm. 
long  and  6  or  8  mm.  in  diameter,  just  above  the  wick  in  the 
flame  of  a  lighted  candle.  Vapours  will  pass  up  the  tube,  and 
may  be  burned  at  the  other  end. 

The  light  and  heat  of  flames  are  not  proportioned  to  each 
other.  The  oxyhydrogen  jet  is  the  hottest  flame  known, 
but  it  gives  out  scarcely  any  light.  If,  however,  a  little  solid 
matter,  such  as  a  piece  of  lime  or  the  stem  of  a  tobacco- 
pipe,  be  introduced,  the  light  becomes  very  intense,  although 
the  effect  of  these  solids  is  to  lower  the  temperature  of  the 
flame.  At  high  temperatures  a  solid  body,  when  heated, 
even  though  it  does  not  burn,  gives  out  light.  At  first  the 
light  is  dull  red;  as  the  heat  increases  it  becomes  yellow, 
then  full  white,  and,  when  extremely  intense,  it  has  a  tinge  of 
violet.  All  our  common  luminous  flames  contain  carbon  in 
the  solid  state,  which,  when  heated  strongly,  gives  out  light, 

Exp.  20 1. — Place  a  cold  saucer  in  a  jet  of  burning  coal  gas  : 
it  is  quickly  covered  with  soot.  Do  the  same  in  a  candle  flame : 


182 


Structure  of  Flame. 


the  saucer  is  blackened.      Try  the  experiment  with  the  scarcely 
luminous  flame  of  a  spirit  lamp  :  no  soot  is  formed. 

The  deposit  of  soot  is  occasioned  by  the  decomposition 
of  olefiant  gas  and  marsh  gas  under  the  influence  of  a  high 
temperature  •  hydrogen  is  partially  separated  from  the  carbon, 
and,  being  more  inflammable,  burns  first,  heating  the  carbon 
intensely.  If  the  carbon  reach  the  oxygen  of  the  air  at  this 
high  temperature,  it  burns  away  also  ;  but  the  cold  surface 
cools  it  before  it  enters  into  combination,  and  so  it  is  deposited. 
Exp.  202. — Kindle  a  common  Argand  gas-burner  and  place 
a  glass  chimney  over  it.  Observe  the  strong  light  it  gives  out. 
Remove  the  chimney,  blow  out  the  flame,  replace  the  chimney, 
covering  the  upper  end  with  a  cap  of  fine  wire  gauze;  then 
kindle  the  gas  above  the  gauze.  The  gas  will  have  become 
mixed  with  air;  it  will  burn  quietly  above  the  gauze,  but  will  not 
give  out  light,  nor  will  it  smoke  a  cold  saucer. 

The  air  burns  the  carbon  and  hydrogen  together  before 
they  can  separate.  What  is  called  Bunsen's  burner  acts  upon 

a  similar  principle ;  it  con- 
sists of  a  jet  of  gas  (a, 
Fig-  63),  which  is  sur- 
rounded by  a  tube  of  metal 
(<:),  at  the  bottom  of  which 
are  openings  for  the  admis- 
sion of  air  (b) ;  the  gas 
passes  up  the  tube,  and 
becomes  mixed  with  the  air 
which  enters  at  the  open- 
ings near  the  bottom,  and 
it  burns  without  smoke 
when  kindled  at  the  top. 
A  sufficient  supply  of  gas  must  be  kept 
up,  or  else  the  flame  will  recede  into 
the  tube,  and  the  gas  will  burn  at  the  bottom. 

The  structure  of  flame  may  be  examined  easily  in  the 
flame  of  a  candle.  It  will  be  seen  to  consist  of  several 
distinct  portions,  as  shown  in  Fig.  64. 


Fig.  63. 


The  Blowpipe.  183 

The  flame  is  maintained  by  the  decomposition  of  the 
melted  wax  or  tallow  which  rises  in  the  wick,  where  it  is 
converted  into  gases  by  the  heat.  At  the  lower  part  of  the 
flame  these  gases  become  at  once  mixed  with  atmospheric 
air,  no  separation  of  carbon  occurs,  and  they  burn  with  a 
pale  blue  light  at  a.  The  greater  part  of  the  combustible 
vapours  are  still  unburned ;  they  rise  above  the  wick,  and 
form  the  central  dark  part  of  the  flame  b.  Here  they  are 
decomposed  by  the  heat  produced  by  the  combustion  of  the 
parts  below.  This  heat  causes  the  separation  of  solid  par- 
ticles of  carbon,  which  become  intensely  hot,  and  give  out 
light  chiefly  in  the  part  marked  c.  This  carbon  itself  burns 
away  gradually  as  it  rises  to  the  surface  of  the  flame,  where 
it  meets  with  fresh  oxygen,  and  disappears 
in  the  form  of  transparent  carbonic  anhy- 
dride d. 

By  directing  a  jet  of  air  into  a  flame  the 
combustion  may  be  rendered  more  active,  and  may 
be  concentrated  into  a  small  space,  so  as  to  afford  a 
very  high  temperature.  It  is  upon  this  principle  that 
that  very  useful  instrument  the  mouth  blow-pipe 
acts.  Fig.  65  shows  a  convenient  form  of  it.  If  by 
its  means  a  current  of  air  be  directed  horizontally 
across  the  flame  a  little  above  the  wick,  the  flame  loses 
its  brilliancy,  and  is  thrown  to  one  side  in  the  form  of 
a  beautiful  pointed  cone  (Fig.  66), in  which  three  dis- 
tinct parts  are  visible.  In  the  centre  is  a  well-marked 
blue  cone  ending  at  a  \  outside  this  is  a  whiter  and 
more  luminous  cone,  and  again  outside  this  brilliant 
cone,  which  ends  at  b,  is  a  third  pale  yellow  flame  c. 
The  different  parts  of  the  flame  vary  in  the  effects  which  they 
produce  ;  the  blue  cone  is  produced  by  the  complete  com 
bustion  of  part  of  the  vapour  in  the  excess  of  oxygen 
supplied  by  the  jet  of  air  to  that  part  of  the  flame.  Beyond 
this  the  combustible  vapour  continually  rising  from  the 
wick  forms  the  luminous  portion,  which  is  very  hot,  and  from 


i  84  Use  of  the  Blowpipe. 

its  containing  an  excess  of  combustible  matter,  is  ready  to 
take  oxygen  from  any  substance  which  is  exposed  to  it.  It 
is  called  the  reducing  flame.  At  the  outer  point  of  the  flame 
the  effects  are  reversed ;  atmospheric  oxygen  is  carried  for- 


Fig.  66. 


ward  by  the  jet  of  flame,  and  becomes  heated  by  it,  so  that 
an  oxidising  action  occurs :  if  a  fragment  of  a  metal  be  ex- 
posed to  the  action  of  this  part  of  the  flame,  it  will  be  con- 
verted into  oxide. 

Exp.  203. — Introduce  a  small  piece  of  common  flint  glass 
tube  into  the  reducing  flame,  between  a  and  b  (Fig.  66),  obtained 
by  blowing  gently  through  a  candle  flame.  The  glass  will  be- 
come opaque  and  black,  because  the  lead  will  be  reduced  from 
the  transparent  form  of  oxide  to  the  opaque  condition  of  metal. 
When  this  has  happened,  place  the  black  portion  just  in  front  of 
the  oxidating  flame  at  c.  The  discolouration  will  slowly  dis- 
appear, and  the  lead  will  recombine  with  oxygen  from  the  air, 
and  again  become  transparent. 

In  skilful  hands  the  blowpipe  enables  the  observer  to 
obtain  quickly  results  of  great  value.  Many  compounds, 
when  heated  on  a  piece  of  charcoal  in  the  reducing  flame, 
immediately  yield  up  their  metallic  basis ;  and  by  the  colour 
of  the  little  bead,  and  its  malleability  or  brittleness,  it  may 
easily  be  known  what  metal  is  present. 

Sometimes  when  the  body  does  not  yield  a  metal  readily,  a 
platinum  wire,  d  (Fig.  66),  bent  into  a  hook  at  one  end,  forms 
a  convenient  support  for  the  substance,  which  should  not 
exceed  a  mustard  seed  in  bulk.  It  will  easily  be  ascertained 
whether  the  substance  melts  ;  whether  it  yields  a  transparent 
an  opaque,  or  a  coloured  bead ;  whether  it  changes  the 


Manufacture  of  Coal  Gas.  185 

colour  of  the  flame,  and  whether  the  effect  of  the  reducing 
flame  differs  from  that  of  the  oxidizing  flame  upon  the  body 
under  examination. 

A  little  borax  or  phosphate  of  sodium  and  ammonium, 
commonly  called  microcosmic  salt,  sometimes  assists  the 
examination. 

When  the  substance  is  placed  on  charcoal  sodic  carbonate 
furnishes  a  flux  which  is  often  very  useful. 

Exp.  204. — Select  a  small  stick  of  charcoal,  and  with  the 
point  of  a  knife  make  a  small  cavity  of  the  size  of  a  split  pea 
upon  the  side  near  one  end.  Put  a  little  white  lead  in  the  cavity, 
and  heat  it  before  the  blowpipe  in  the  reducing  flame.  A  little 
bead  of  lead  will  easily  be  obtained,  surrounded  by  a  border  of 
yellow  lead  oxide.  The  lead  will  flatten  under  the  hammer. 

Exp.  205. — Place  in  a  cavity  in  another  piece  of  charcoal  a 
small  fragment  of  copper  oxide,  with  about  its  own  bulk  of  sodic 
carbonate.  The  metal  will  require  a  stronger  heat,  but  may 
be  reduced  in  like  manner.  If  the  little  bead  be  placed  between 
two  folds  of  paper  it  may  be  flattened  with  the  hammer,  and 
will  show  the  red  colour  of  copper. 

Coal  gas. — Certain  kinds  of  coal,  such  as  cannel  coal  and 
the  bituminiferous  house  coal  used  in  London,  when  heated, 
undergo  decomposition,  their  constituents  rearrange  them- 
selves in  new  forms,  and  give  out  a  large  quantity  of  gas, 
which  burns  with  brilliant  jets  of  flame.  If  such  coal,  instead 
of  being  allowed  to  burn  in  the  open  fire,  is  heated  out  of 
the  air  in  iron  or  clay  retorts  provided  with  an  escape-tube, 
a  large  quantity  of  gas  may  be  collected,  ard  may  be  used 
for  illuminating  or  heating  purposes.  This  is  the  common 
process  of  making  coal  gas.  The  products  obtained  by 
heating  coal  in  this  manner  are  very  numerous.  The  solid 
residue  in  the  retort,  after  the  volatile  matters  have  been 
driven  off,  constitutes  '  gas  coke.'  Among  the  volatile 
matters  are  water,  along  with  which  condense  the  sulphide 
and  carbonate  of  ammonium ;  besides  this  there  is  a  dense 
black  offensive  viscid  liquid,  known  as  coal  tar,  which  is  a 


1 86  A  nalysis  of  CoaL 

very  complex  mixture,  chiefly  consisting  of  hydrocarbons  and 
carbolic  acid ;  some  portions  of  these  hydrocarbons  supply 
the  material  from  which  aniline,  the  basis  of  most  of  the  coal- 
tar  dyes,  is  procured.  The  gaseous  products  are  also  very 
numerous  ;  among  them  are  olefiant  gas,  and  some  other 
gases  of  greater  density,  but  of  a  similar  character,  which 
furnish  the  most  important  illuminating  constituents;  marsh 
gas,  hydrogen,  and  carbonic  oxide  are  also  present;  but 
they  have  little  illuminating  power.  There  are  also  small 
quantities  of  sulphuretted  hydrogen,  carbonic  anhydride, 
cyanogen,  and  carbon  disulphide,  all  of  which  it  is  the 
object  of  the  gas-maker  to  remove.  This  is  done  by  pass- 
ing the  gas  over  hydrated  ferric  oxide  and  slaked  lime ;  the 
iron  oxide  removes  the  sulphuretted  hydrogen  and  cyanogen, 
while  the  carbonic  anhydride  is  stopped  by  the  lime.  The 
gas,  when  thus  purified,  is  washed  with  water  to  get  rid  of 
small  quantities  of  ammonia,  and  is  afterwards  stored  up  in 
vast  iron  reservoirs  or  gas-holders,  from  which  it  is  dis- 
tributed for  consumption. 

The  removal  of  the  sulphur  compounds  is  especially  neces- 
sary; because,  when  burned,  they  furnish  sulphurous  and 
sulphuric  acids,  which  are  very  injurious  to  furniture,  books, 
and  paintings  exposed  to  their  action.  The  other  materials 
furnish  only  water  and  carbonic  anhydride,  when  burned 
with  a  sufficient  supply  of  air. 

Coal  gas  has  a  peculiar  offensive  odour,  due  in  part  to  a 
compound  of  carbon  and  hydrogen  called  acetylene  (C2H2). 
If  coal  gas  escape  into  the  atmosphere,  it  forms  an  explosive 
mixture.  Hence,  if  a  smell  of  gas  be  perceived  in  a  room, 
no  light  must  be  admitted;  the  supply  of  gas  should  be  at 
once  shut  off  from  the  main,  and  the  doors  and  windows 
thrown  open  to  ventilate  the  house  or  the  room.  After- 
wards the  cause  of  the  escape  may  be  sought. 

Exp.  206. — Place  15  or  20  grams  of  coal  in  small  fragments 
in  a  tube  of  Bohemian  glass,  a  (Fig.  67),  18  or  20  centimetres 
long,  and  sealed  at  one  end ;  to  the  other  end  fit  a  good  cork, 


Destructive  Distillation  of  Coal.  187 

through  which  passes  a  quill  tube  bent  at  a  right  angle,  and 
fitted  into  a  phial  (b\  In  one  limb  of  the  bent  tube  (V)  place  a 
piece  of  reddened  litmus  paper;  in  the  other  (d\  a  piece  of 
filtering-paper  moistened  with  a  solution  of  lead  acetate.  Plac£ 
a  little  limewater  in  the  test-tube  e^  and  collect  the  gas  which 
comes  over  in  a  gas  jar  (/)  provided  with  a  stop-cock.  Heat 
the  tube  a  gradually  by  placing  it  in  a  tray  of  coarse  wire 
gauze,  and  surrounding  it  with  lighted  charcoal ;  let  it  rise  to 

Fig.  67. 


dull  redness.  Tar  will  become  condensed,  mixed  with  water 
in  b,  the  red  litmus  in  c  will  become  blue  from  the  ammonia,  the 
lead  salt  will  be  blackened  by  the  sulphuretted  hydrogen,  the  lime- 
water  rendered  milky  by  the  carbonic  acid,  while  an  inflammable 
gas  will  be  collected  in  the  jar,  and  may  be  burned  by  transferring 
the  jar  to  the  deep  part  of  the  trough,  depressing  it  in  the  water, 
and  lighting  the  gas  as  it  escapes  on  gradually  opening  the  stop- 
cock. Coke  will  be  left  in  the  glass  tube. 

Exp.  207. — Hold  a  cold  wide  glass  tube,  of  a  metre  or  more 
in  length,  over  a  jet  of  burning  coal  gas  :  moisture  will  speedily 
become  condensed  on  the  cold  sides  of  the  tube,  owing  to  the 
formation  of  water  by  the  burning  of  the  hydrogen. 

Exp.  208. — Pour  a  little  limewater  into  the  tube,  having  closed 
one  end  with  the  hand  after  withdrawing  it  from  the  flame  :  the 
limewater  will  become  turbid  by  absorbing  carbonic  acid. 

A  single  jet  of  coal  gas,  consuming  about  136  litres 
(5  cubic  feet)  of  gas  per  hour,  will  produce  nearly  a  quarter 
of  a  litre  of  water  as  it  bums. 


1 88  Cyanogen. 

(41)  CYANOGEN:  Symb.  Cn  or  Cy;  ReL  and  Atom.  Wt. 
26;  Mol.  Wt.  52;  Mol.  Vol.  ["T1,  Cy2;  £/.  Gr.  rSo6. 

This  is  the  name  given  to  the  compound  which  carbon 
forms  with  nitrogen,  the  '  blue  producer,'  owing  to  its  being 
the  characteristic  component  of  Prussian  blue.  The  two 
elements  do  not  combine  directly ;  but  if  nitrogen  gas  be 
passed  over  a  red-hot  mixture  of  charcoal  and  potassic  car- 
bonate, the  carbon  and  nitrogen  unite  with  the  potassium, 
while  carbonic  oxide  escapes — 

K2C03  +  4C  +  N2     =     2KCN   +   3CO. 

Cyanogen  is  always  one  of  the  products  obtained,  in  small 
quantities,  during  the  distillation  of  pit  coal ;  but  its  com- 
pounds are  usually  obtained  from  the  cyanide  of  iron  and 
potassium,  which  crystallises  in  large  yellow  tables,  and  is 
known  as  potassic  ferrocyanide  or  prussiate  of  potash 
(K4FeCy6,  3H2O). 

This  salt  is  prepared  by  heating  to  dull  redness,  in  a  covered 
iron  pot,  about  5  parts  of  parings  of  horns,  hides,  hoofs,  or 
other  animal  refuse,  with  2  parts  of  pearlash  and  iron  filings. 
The  nitrogen  and  carbon  combine  at  the  high  temperature, 
and  unite  with  the  iron  and  a  portion  of  reduced  potassium. 

If  this  salt  be  dissolved  in  water  and  distilled  with  diluted 
sulphuric  acid,  the  intensely  poisonous  prussic  or  hydro- 
cyanic acid  comes  over,  and  the  distilled  liquid,  if  saturated 
with  mercuric  oxide,  furnishes  mercuric  cyanide  (HgCy2); 
which,  if  thoroughly  dried,  and  heated  in  a  test-tube,  becomes 
decomposed  into  metallic  mercury  and  cyanogen  gas — 
HgCy2  =  Hg  +  Cy2. 

Cyanogen  is  a  transparent,  colourless  gas,  with  a  peculiar 
penetrating  odour.  It  is  very  poisonous,  and  is  combustible. 
If  a  jet  of  the  gas  be  kindled,  it  burns  with  a  characteristic 
rose-edged  purple  flame.  It  is  soluble  in  water  and  in 
alcohol. 

The  peculiar  character  of  cyanogen  is  its  property,  though 
a  compound,  of  combining  with  the  metals  like  one  of  the 


Hydrocyanic  A  cid.  1 89 

halogens.  Potassium  when  heated  in  the  gas  combines 
with  it,  and  forms  potassic  cyanide.  This  circumstance  has 
given  rise  to  the  theory  of  compound  radicals*  now  so  exten- 
sively applied  in  organic  chemistry,  cyanogen  being  the  first 
of  these  radicals  which  was  obtained. 

Cyanogen  forms  with  hydrogen  an  acid  compound — the 
intensely  poisonous  hydrocyanic  acid  (HCy),  which,  however, 
cannot  be  obtained  by  the  direct  union  of  its  components. 
The  vapour  of  this  acid  contains  one  volume  of  hydrogen 
and  one  of  cyanogen,  united  without  condensation,  as  in  the 
case  of  hydrochloric  acid,  and  the  hydrogen  acids  of  the 
other  halogens.  It  is  a  very  volatile  liquid,  which  boils  at 
26*5°  C.  ;  but  on  account  of  its  poisonous  character,  it  is 
rarely  prepared  in  a  pure  state.  The  vapour  is  inflammable, 
and  burns  with  a  whiter  flame  than  that  of  cyanogen,  which 
it  resembles  in  appearance. 

In  a  diluted  state  it  is  obtained  by  distilling  a  solution  of 
the  cyanide  or  of  the  ferrocyanide  of  potassium  with  diluted 
sulphuric  acid,  taking  care  that  the  vapours  are  carried  away 
at  once  by  a  brisk  current  of  air — 

KCy  +  H2SO4     =     HCy  +   KHSO4. 

It  is  better  not  to  make  these  experiments  without  the  aid  of 
some  person  of  experience. 

The  solution  of  this  acid  has  an  odour  resembling  that  of 
peach-blossoms.  Its  acid  properties  are  feeble ;  it  does  not 
neutralise  potash  perfectly,  but  dissolves  mercuric  oxide  very 
readily ;  and  it  gives  a  white  precipitate  of  argentic  cyanide 
( AgCy)  when  mixed  with  a  solution  of  argentic  nitrate.  A 
good  test  of  the  acid  is  to  add  a  slight  excess  of  potash,  and 
then  a  mixture  of  ferrous  and  ferric  sulphate.  A  mixed  pre- 
cipitate of  ferrous  and  ferric  oxide  is  thus  formed ;  and  this, 

*  By  the  term  radical  is  meant  any  substance  which  by  uniting  with 
a  metal  forms  a  salt,  or  with  hydrogen  forms  an  acid.  In  NaCl  or 
common  salt,  chlorine  is  the  simple  radical ;  in  HNO3  or  nitric  acid, 
NO3  or  nitrion  is  the  compound  radical.  So  in  KCN  or  potassic 
cyanide,  CN  is  the  compound  radical. 


190  Compounds  of  Cyanogen. 

on  adding  hydrochloric  acid  in  slight  excess,  to  redissolve  the 

excess  of  oxides  of  iron,  leaves  Prussian  blue  (Fe4,  Fe3Cyl8) — 

iSKCy  +  3FeO,  2Fe2O3  +  iSHCl 

=  iSKCl  +  9H20  +  Fe4Fe3Cyl8. 

Hydrocyanic  acid,  mixed  with  a  peculiar  essential  oil,  is 
obtained  by  distillation  from  the  kernels  of  the  bitter  almond, 
and  many  kinds  of  stone  fruit,  after  they  have  been  crushed 
and  mixed  with  water.  The  juice  of  the  tapioca  plant  also 
contains  it.  It  is  also  present  in  the  water  distilled  off  the 
leaves  of  the  laurel,  the  peach,  and  several  other  shrubs. 

Many  cyanides  of  the  common  metals  are  insoluble  in 
water,  but  are  readily  dissolved  by  solutions  of  the  cyanide 
of  potassium  or  of  sodium.  The  double  cyanides  thus 
obtained  are  numerous,  and  some  of  them  very  remarkable. 
The  simple  cyanides  are  intensely  poisonous,  and  require 
great  care  in  experimenting  with  them. 

Exp.  209. — Dissolve  3  or  4  decigrams  of  potassic  cyanide  in 
about  ten  times  their  weight  of  water.  Add  a  few  drops  to  a  small 
quantity  of  a  solution  of  argentic  nitrate  in  a  test-tube.  At  first  a 
copious  white  precipitate  of  argentic  chloride  will  be  formed — 

KCy   +   AgN(>3     =     AgCy   +    KNO3, 

and  on  further  additions  of  the  cyanide  the  precipitate  will  be 
gradually  dissolved,  AgCy,  KCy  being  formed. 

Exp.  210. — Melt  2  grams  of  potassic  cyanide  in  a  small  iron 
spoon,  and  add  a  little  litharge  till  the  salt  becomes  slightly 
yellow.  A  bead  of  metallic  lead  will  be  formed,  and  the  cyanide 
will  have  become  converted  into  cyanate — 

PbO    +    KCy     =     Pb   +   KCyO. 

Potassic  cyanide,  in  consequence  of  this  tendency  to 
absorb  oxygen,  is  often  used  to  reduce  the  metals  from  their 
oxides  as  a  test  in  the  laboratory. 

Cyanogen  forms  a  large  number  of  other  important  com- 
pounds, but  they  are  properly  to  be  studied  among  the 
products  of  organic  chemistry. 

(42)  The  Atomic  theory. — In  the  foregoing  pages  the 
terms  atom,  atomic  weight,  and  molecule  have  been  frequently 


The  Atomic  Theory.  191 

used.  It  will  be  necessary  now  to  consider  more  exactly 
what  these  expressions  mean. 

Chemists  assume  that  though  every  visible  fragment  of 
any  elementary  body  admits  of  further  division  into  a  vast 
multitude  of  minute  particles,  there  is  a  limit  beyond 
which  this  process  of  subdivision  cannot  be  carried  by  any 
known  method,  whether  chemical  or  mechanical.  These 
ultimate  or  indivisible  particles  are  what  are  called  the 
atoms  of  the  element.  No  one  has  ever  seen  an  atom, 
since  such  bodies  are  far  more  minute  than  the  smallest 
fragments  visible  by  the  aid  of  our  strongest  magnifying 
glasses.  The  atoms  of  any  particular  element  are  further 
supposed  to  be  exactly  equal  to  each  other  in  size  and  in 
weight;  and  when  at  the  same  temperature,  to  be  abso- 
lutely similar  one  to  another  in  all  respects.  But  the  atoms 
of  any  single  element  differ  from  those  of  all  the  other 
elements  in  chemical  properties  as  well  as  in  weight. 
Further,  whenever  chemical  combination  takes  place  be- 
tween any  two  chemical  elements,  it  is  assumed  that  union 
occurs  between  their  separate  atoms.  This  chemical  union 
is  far  more  intimate  than  that  effected  by  the  force  of  co- 
hesion which  forms  them  into  solids,  still  more  than  that 
mechanical  mixture  by  which  they  are  converted  into  masses 
or  heaps  of  powder ;  and  the  difference  between  combination 
and  mechanical  mixture  is  that  the  atoms,  being  in  the  case 
of  true  combination  held  together  by  chemical  force,  cannot 
be  separated  by  mechanical  means;  while  such  separation 
is  practicable  more  or  less  completely  when  the  two  bodies 
are  merely  mixed  mechanically,  and  therefore  imperfectly, 
and  often  more  or  less  irregularly. 

These  assumptions  as  to  the  atomic  constitution  of  matter 
have  been  made  with  a  view  of  explaining  the  quantitative 
laws  which  regulate  chemical  combination.  This  theory 
of  the  finite  and  definite  divisibility  of  matter,  or  divisibility 
of  matter  down  to  a  fixed  limit,  is  in  fact  the  only  one 
hitherto  conceived  by  which  union  in  definite  proportion  is 


1 92    Law  of  Definite  and  Multiple  Proportions,  &c. 

accounted  for ;  and  if  these  suppositions  be  admitted,  the 
known  laws  of  chemical  combination  follow  from  them  as  a 
matter  of  necessity. 

These  laws  are  as  follow : — 

1.  The  law  of  definite  proportions. — Whenever  such  com- 
bination occurs  between  two  elements  as  to  form  any  given 
compound,  the   proportions  must  be   definite,   since  these 
proportions  are  determined  by  the  relative  weights  of  the 
atoms  of  the  combining  elements,  and  the  atom  cannot  be 
subdivided. 

2.  The   law   of  multiple   proportions. — When   the  same 
pair  of  elements  unite  in  several  different  proportions,  these 
proportions  must  vary  according  to  the  terms  of  a  simple 
series  of  multiples,  since  each  atom  of  one  element  must 
unite  with  one,  with  two,  or  with  three  atoms  of  the  other 
element,  or  in  some  other  ratio  almost  equally  simple,  be- 
cause the  atom  does  not  admit  of  subdivision. 

3.  The  law  of  equivalent  proportions. — Combination  must 
also  occur  in  equivalent  proportions,  since  the  amount  of 
each  element  which  is  capable  of  displacing  any  of  the  other 
elements  must  be  in  the  proportion  of  the  weight  of  the 
atom  of  the  displacing  element,  or  of  a  simple  multiple  of 
that  weight,  and  the  atom  cannot  be  subdivided. 

4.  The  law  of  molecular  weights. — In  every  compound 
body  the  molecular  weight,  or  weight  of  the  smallest  particle 
of  the  compound  which  can  exist,  is  necessarily  that  obtained 
by  adding  together  the  weights  of  all  the  atoms  of  the  several 
elements  which  have  united  together  to  form  the  molecules 
of  the  compound  body,  since  none  of  the  atoms  of  the  con- 
stituent elements  can  be  subdivided. 

Suppose,  for  example,  that  each  atom  of  oxygen  weigh 
1 6  times  as  much  as  each  separate  atom  of  hydrogen;  that 
the  atom  of  chlorine  weighs  35*5  times  as  much,  the  atom 
of  nitrogen  14  times  as  much,  the  atom  of  bromine  80  times 
as  much,  the  atom  of  silver  108  times  as  much,  and  the 
atom  of  mercury  200  times  as  much ;  exactly  as  is  repre- 


Chemical  Equivalents.  193 

sented  in  the  column  headed  *  Atomic  Weights'  in  the  table 
at  page  198. 

It  follows  that  when  chlorine  and  hydrogen  unite  to  form 
hydrochloric  acid,  if  one  atom  of  each  element  enters  into 
the  formation  of  each  molecule  of  the  compound  (HC1), 
hydrochloric  acid  must  necessarily  and  invariably  contain  in 
every  36*5  parts  by  weight,  whether  it  be  grams,  pounds,  or 
tons,  i  part  of  hydrogen  and  35*5  parts  of  chlorine. 

In  like  manner,  if  each  of  the  molecules  of  argentic  bro- 
mide be  formed  by  the  union  of  i  atom  of  silver  with  i  of 
bromine  (AgBr),  then  188  parts  by  weight  of  this  bromide 
will  necessarily  consist  of  108  parts  of  silver  and  80  of 
bromine. 

Again,  if  each  molecule  of  water  consist  of  2  atoms  of 
hydrogen  and  i  atom  of  oxygen  (H2O),  it  must  happen  that 
1 8  parts  by  weight  of  water  will  always  contain  2  parts  by 
weight  of  hydrogen  and  16  parts  by  weight  of  oxygen. 

Suppose  next  that  argentic  bromide  be  heated  in  a  stream 
of  chlorine  gas;  the  bromine  will  be  displaced  by  the 
chlorine,  and  argentic  chloride  will  be  formed.  Now  if 
each  molecule  of  argentic  chloride  (AgCl)  be  formed  by  the 
union  of  i  atom  of  silver  with  i  of  chlorine,  the  bromine 
displaced  must  be  in  the  proportion  of  80  parts  of  bromine 
for  every  35-5  of  chlorine  which  unite  with  the  silver;  that 
is  to  say,  35-5  parts  of  chlorine  are  equivalent  in  combination 
to  80  parts  of  bromine. 

It  was  at  one  time  supposed  that  the  chemical  equivalent 
of  the  elements  always  represent  the  relative  weights  of  their 
atoms,  so  that  the  term  atomic  weight  was  often  used  instead 
of  that  of  chemical  equivalent ;  but  the  two  terms  involve 
ideas  which  are  essentially  distinct.  A  simple  substance 
can  have  but  one  atomic  weight,  but  it  may  have  two  or 
more  chemical  equivalents  ;  for  instance,  mercury  forms  two 
compounds  with  chlorine,  viz.  calomel  and  corrosive  sub- 
limate. In  calomel  200  grams  of  mercury  are  combined 
with  35-5  grams  of  chlorine  ;  whilst  in  corrosive  sublimate 

o 


194  Law  of  Volumes. 

the  200  of  mercury  are  united  with  71  grams  of  chlorine, 
or  twice  as  much  •  and  this  is  explained  upon  the  sup- 
position that  the  atom  of  mercury  is  in  calomel  united  with 
i  atom  of  chlorine  (HgCl),  whilst  in  corrosive  sublimate 
it  is  united  with  2  atoms  (HgCl2).  But  if  we  compare  the 
quantity  of  mercury  in  each  compound  with  the  same  weight, 
35-5,  of  chlorine,  we  find  in  calomel  that  200  parts  of 
mercury  are  equivalent  to  35*5  parts  of  chlorine ;  whilst  in 
corrosive  sublimate  100  parts  of  mercury  are  equivalent  to 
the  same  35*5  parts  of  chlorine  ;  consequently  mercury  has 
two  different  equivalents  in  the  two  compounds. 

Again,  in  the  five  oxides  of  nitrogen  we  have  an  excellent 
example  of  multiple  proportion.  If  2  atoms  of  nitrogen  are 
supposed  in  each  case  to  be  concerned,  we  find  the  com- 
position of  each  represented  by  the  following  numbers : 
nitrous  oxide  contains  in  every  44  parts  28  parts  of  nitrogen 
and  1 6  of  oxygen,  or  2  atoms  of  nitrogen  and  i  of  oxygen  ; 
nitric  oxide  in  every  60  parts  contains  28  parts  of  nitrogen 
and  3  2  of  oxygen,  or  2  atoms  of  nitrogen  and  2  of  oxygen ; 
nitrous  anhydride  in  every  76  parts  contains  28  of  nitrogen 
and  48  of  oxygen,  or  2  atoms  of  nitrogen  and  3  of  oxygen ; 
nitrogen  peroxide  in  every  92  parts  contains  28  of  nitrogen 
and  64  of  oxygen,  or  2  atoms  of  nitrogen  and  4  of  oxygen  ; 
while  nitric  anhydride  in  every  108  parts  contains  28  of 
nitrogen  and  80  of  oxygen,  or  2  atoms  of  nitrogen  and  5  of 
oxygen ;  the  series  being  represented  as  N2O,  N2O2,  N2O3, 
N2O4,  and  N2O5. 

It  has  been  ascertained  that  equal  measures  or  volumes 
of  every  gas  and  every  vapour  taken  at  a  sufficient  distance 
from  its  boiling  point,  no  matter  whether  simple  or  com- 
pound, expand  equally  for  an  equal  rise  of  temperature,  if 
both  are  compared  under  equal  pressures,  and  at  the  same 
temperatures.  It  is  also  true  that  all  gases  and  vapours 
expand  or  contract  equally  when  equal  volumes  of  the 
different  gases  are  submitted,  at  the  same  temperatures,  to 
an  equal  diminution  or  increase  of  pressure.  Hence  it 


Atomic  Weights.  195 

appears  to  be  a  necessary  conclusion  that  equal  volumes  of 
all  gases  contain  an  equal  number  of  molecules,  whether 
those  molecules  be  simple  or  compound.  Further,  the 
molecules  of  the  same  substance  are  all  absolutely  similar  to 
each  other  in  size,  weight,  and  chemical  properties,  if  com- 
pared under  similar  circumstances. 

The  term  molecular  volume  is  used  to  signify  the  space 
occupied  by  a  molecule  of  the  body  in  the  form  of  gas  or 
vapour,  compared  with  that  of  the  atom  of  hydrogen,  or  the 
atomic  volume  of  hydrogen.  Now  the  volume  of  the  molecule 
of  a  compound  body  in  the  aeriform  state  [  [~|  is  exactly 
double  the  volume  of  the  atom  of  hydrogen  [H|. 

The  atom  is  defined  to  be  the  smallest  and  chemically 
indivisible  particle  of  each  element  which  can  exist  in  a 
compound,  united  with  other  particles,  either  of  the  same  or 
of  different  elements,  but  which  is  not  known  in  a  separate 
form  ;  and  the  molecule  of  an  element  is  defined  to  be  the 
smallest  quantity  of  that  elementary  substance  supposed  to 
be  capable  of  existing  in  a  separate  form.  If  H,  for  instance, 
represent  the  atom  of  hydrogen,  H2  will  represent  its  mole- 
cule. Each  molecule  of  chlorine  and  of  the  other  allied 
elements  when  in  the  gaseous  state  appear,  for  reasons  to 
be  explained  immediately,  to  consist  of  two  atoms.  When 
a  molecule  of  hydrogen  is  made  to  react  chemically  upon 
a  molecule  of  chlorine,  two  molecules  of  hydrochloric  acid 
are  formed,  the  half  molecule  of  hydrogen  exchanging  places 
with  the  half  molecule  of  chlorine — 

|H;H|      +     |C1  Cl|  becoming  |HCl|     +     |HCI|. 

It  will  be  desirable  to  develop  these  considerations  a  little 
more  fully.  The  number  adopted  for  the  atomic  weight  of 
any  element  is  based  upon  a  careful  chemical  analysis  of 
several  compounds  of  that  element.  Suppose,  for  example, 
the  atomic  weight  of  copper  to  be  the  subject  of  experiment, 
and  that  a  quantity  of  the  pure  oxide  of  the  metal  has  been 
prepared,  and  a  portion  carefully  weighed,  and  heated  in 

O   2 


196  Determination  of  Atomic  Weights. 

a  stream  of  pure  hydrogen  gas.  The  hydrogen  gradually 
removes  all  the  oxygen  in  the  form  of  steam,  leaving  nothing 
but  pure  copper  behind.  On  weighing  this  copper,  the 
quantity  of  oxygen  originally  combined  with  it  in  the  oxide 
is  ascertained  by  the  loss  of  weight  experienced.  Then  the 
relative  proportions  between  the  combining  proportion  of 
copper  and  oxygen,  referred  to  hydrogen  as  the  unit,  can 
be  easily  calculated. 

But  this  determination  would  not  be  sufficient  to  settle 
the  atomic  weight  if  taken  alone,  even  if  other  analyses  of 
this  same  oxide  and  of  other  compounds  of  copper  gave 
results  which  showed  that  the  experiments  had  been  made 
with  exactness.  It  is  necessary  also  to  know  the  number  of 
atoms  in  the  molecule  of  the  different  compounds  of  the 
substances  analysed;  whether,  for  instance,  the  number  of 
atoms  of  copper  in  the  molecule  of  its  oxide  be  one  of 
copper  to  one  of  oxygen,  two  of  copper  to  one  of  oxygen, 
or  two  of  oxygen  to  one  of  copper,  two  of  copper  to  three  of 
oxygen,  or  any  other  proportion.  In  the  case  of  solid 
bodies,  not  convertible  easily  into  vapour,  this  determination 
is  often  attended  with  difficulty  and  uncertainty.  There  are, 
however,  various  considerations  by  which  this  conclusion 
may  be  arrived  at  with  more  or  less  probability.  One  of  the 
best  methods  consists  in  comparing  together  all  the  com- 
pounds of  the  element  under  examination,  for  the  purpose  of 
rinding  out  the  smallest  proportion  in  which  that  element 
enters  into  any  compound  molecule,  for  this  must  repre- 
sent its  atom,  by  the  definition  of  the  word  which  we  have 
adopted. 

In  cases  where  bodies  can  be  converted  into  vapour,  this 
task  is  much  facilitated  by  that  very  circumstance.  For 
example,  a  large  number  of  compounds  of  hydrogen  have 
been  analysed.  Most  of  them  may  be  obtained  in  the  form 
of  gas  or  vapour ;  in  which  case  their  specific  gravities  in  the 
aeriform  condition  may  be  ascertained  by  experiment.  From 
these  specific  gravities  the  relative  weights,  or  weights  com- 


Atomic  and  Molecular  Weights. 


197 


pared  with  that  of  an  equal  bulk  of  hydrogen,  and  the 
molecular  weights  are  at  once  easily  obtained. 

Some  of  the  more  important  of  these  compounds  have 
been  already  described,  and  they  are  mentioned  in  the 
following  list : — 


Compounds  of  Hydrogen 

Molecular 
Volume 

Weights 
referred  to 
Hydrogen 

Weights  of 
Hydrogen 
in  Molecule 

Hydrochloric  Acid 

m 

3^5 

I 

Hydrobromic  Acid 

m 

8ro 

I 

Hydrogen  Gas     . 

ED 

2'O 

2 

Water         .... 

ED 

18-0 

2 

Sulphuretted  Hydrogen 

1  _:  ] 

34*0 

2 

Ammonia   .... 

CD 

17-0 

3 

Phosphuretted  Hydrogen     . 

CD 

34'Q 

3 

Olefiant  Gas 

CD 

28-0 

4 

Marsh  Gas  .... 

ED 

1  6-0 

4 

Now  if  the  molecule  of  hydrogen  weigh  2,  the  smallest 
weight  of  hydrogen  which  is  contained  in  an  equal  volume 
of  vapour  of  any  of  the  compounds  of  hydrogen  in  this  list, 
and  it  may  be  added  in  any  others  that  are  known,  is  half 
that  amount,  or  i.  Hence  chemists  have  concluded  that 
this  quantity  of  hydrogen  is  the  smallest  that  can  enter  into 
combination,  or,  according  to  the  supposition  with  which  we 
began,  that  it  is  to  be  regarded  as  the  atom  of  hydrogen. 
Now  hydrogen  has  the  smallest  combining  number  of  any 
element  known,  so  that  it  has  been  found  convenient  to 
take  the  hydrogen  number  as  i,  or  the  unit  of  the  scale  with 
which  the  atomic  weights  of  all  the  other  elements  are  com- 
pared, as  has  been  done  in  the  table  given  at  page  198  ;  so 


198 


The  Metals. 


that  supposing  the  weight  of  the  atom  of  hydrogen  to  be 
known,  the  atomic  weight  of  any  other  element  would  be  the 
number  which  represents  how  many  times  this  atom  is 
heavier  than  the  atom  of  hydrogen. 

The  following  table  contains  a  list  of  such  of  the  elemen- 
tary bodies  as  have  been  converted  into  vapour  in  such  a 
manner  as  to  admit  of  determining  their  specific  gravity  in 
that  form,  and  thus  of  ascertaining  the  number  of  atoms  in 
the  molecule,  on  the  supposition  that  equal  volumes  of  every 
gas  or  vapour  contain  an  equal  number  of  molecules  : — 


Element 

Atomic 
Weights 

Weights  of 
equal 
Volumes 
of  Vapour 

Atoms  in 
i  Molecule 

Specific  Gravity  of  Vapour 

Observed 

Calculated 

Cadmium 

112 

56 

I 

3*94 

3-8690 

Zinc 

65 

32-5 

I 

Mercury 

200 

IOO 

I 

6-976 

6-9101 

Hydrogen 

I 

I 

2 

0-0692 

0*0691 

Chlorine 

35'5 

35'5 

2 

2-47 

2-4531 

Bromine 

80 

80 

2 

5'54 

5-5281 

Iodine    . 

127 

127 

2 

8716 

8-7560 

Oxygen  . 

16 

16 

2 

1-1056 

1-1056 

Sulphur. 

32 

32 

2 

2-23 

2-2168 

Selenium 

79*5 

79'5 

2 

5-68 

5-4680 

Tellurium 

129 

129 

2 

9'oo 

8-9130 

Nitrogen 

H 

H 

2 

0-9713 

0-9674 

Phosphorus 

3i 

62 

4 

4-42 

4-2840 

Arsenicum 

75 

150 

4 

10-60 

10-1670 

CHAPTER  XL 
B.    THE    METALS. 

(43)  The  Metals  in  General. — There  is  no  absolute  dis- 
tinction between  the  non-metals  and  the  metals,  but  the 
subdivision  is  practically  convenient,  and  it  is  usual  to  con- 
sider a  body  which  has  a  high  lustre,  great  opacity,  and  is  a 


Melting  Points  of  Metals. 


199 


good  conductor  of  heat  and  electricity,  as  a  metal.  But  on 
the  one  hand,  graphite,  although  it  has  all  these  properties, 
is  not  reckoned  amongst  the  metals  ;  and  on  the  other, 
arsenicum  and  tellurium,  though  possessing  them,  are  by 
some  chemists  considered  as  non-metals. 

The  metals  differ  very  much  in  chemical  properties  ; 
some,  like  potassium  and  sodium,  have  an  intense  attraction 
for  oxygen,  whilst  others,  like  gold  and  silver,  have  but  a 
feeble  attraction  for  it.  As  a  rule,  the  lighter  metals  are 
those  which  are  most  easily  oxidized.  In  the  following  table 
the  lightest  metals  are  placed  first.  The  metals  exhibit  a 
very  great  variation  in  density.  Three  of  them  are  light 
enough  to  float  in  water,  and  lithium  is  lighter  than  any 
known  liquid,  while  platinum  is  the  heaviest  of  all  known 
substances. 

SPECIFIC  GRAVITIES  AND  FUSING  POINTS  OF  METALS. 


Specific 
Gravity 

Fusing 
Point 

Specific 
Gravity 

Fusing 
Point 

Lithium     . 

0-593 

1  80° 

Molybdenum 

8-62 

Potassium  . 

0-865 

62-5 

Nickel 

8-82 

Sodium 

0-972 

97-6 

Copper 

8-95 

I0900 

Rubidium  . 

I-52 

38-5 

Cobalt 

8-95 

Calcium     . 

I-578 

Bismuth 

9-80 

264 

Magnesium 

I'743 

Silver 

iQ'53 

1023 

Glucinium  . 

2-1 

Lead 

11-36 

325 

Strontium  . 

2-54 

Ruthenium 

1  1-4 

Aluminum 

2-67 

Palladium 

n-8 

Arsenicum 

5*95 

Thallium 

11-9 

294 

Tellurium  . 

6-25 

Rhodium 

I2'I 

Antimony  . 

6-71 

450 

Mercury 

I3-596 

-39 

Chromium 

6-81 

Tungsten 

17-6 

Zinc  . 

7-I5 

412 

Uranium 

18-4 

Tin   . 

7-29 

228 

Gold. 

I9-34 

IIO2 

Iron  . 

7-84 

Iridium 

21-15 

Manganese 

8-01 

Osmium 

21-4 

Cadmium  . 

8-69 

228 

Platinum 

21-53 

The  melting  points  of  the  metals  also  vary  very  widely.  In 
the  table  the  melting  points  of  all  the  metals,  so  far  as  they 
have  been  ascertained,  are  given.  Mercury  is  liquid  at  all 


2OO  Properties  of  the  Metals. 

ordinary  temperatures  ;  potassium  and  sodium  melt  beneath 
the  boiling  point  of  water.  Zinc  melts  below,  and  copper 
above,  a  red  heat ;  silver,  gold,  and  copper  require  a  very 
bright  red  heat  to  fuse  them.  Cast  iron  melts  at  about 
1500°,  and  wrought  iron  not  lower  than  i8oo°C.  Cobalt, 
nickel,  and  wrought  iron  require  the  strongest  heat  of  the 
forge  to  melt  them.  Molybdenum,  chromium,  tungsten, 
and  palladium  do  not  completely  melt  even  at  this  tempera- 
ture ;  and  platinum,  rhodium,  iridium,  vanadium,  ruthenium, 
and  osmium  cannot  be  melted  but  in  the  heat  of  the  oxy- 
hydrogen  blowpipe,  or  that  of  the  voltaic  arc. 

Some  few  of  the  metals  may  be  converted  into  vapour 
readily,  and  are  ordinarily  purified  by  distillation.  Mer- 
cury, arsenicum,  tellurium,  cadmium,  zinc,  magnesium,  potas- 
sium, sodium,  and  rubidium  are  thus  purified.  Mercury 
boils  at  350°  C.  Arsenicum  is  volatilised  below  redness. 
Cadmium  requires  a  full  red  heat  (860°),  at  which  point  it 
boils,  and  may  be  distilled  ;  and  the  boiling  point  of  zinc, 
though  as  high  as  1040°,  is  equally  fixed.  Potassium,  sodium, 
magnesium,  and  rubidium  require  a  still  higher  temperature, 
which  has  not  been  measured. 

Many  of  the  other  metals,  including  silver  and  gold,  may 
be  volatilised  by  the  intense  heat  of  the  sun's  rays  when 
brought  to  a  focus  by  a  very  large  convex  lens. 

Several  of  the  metals  when  rubbed  give  out  a  character- 
istic odour,  as  is  the  case  with  iron,  tin,  and  copper.  Arse- 
nicum, when  volatilised,  emits  a  strong  odour  of  garlic. 
The  taste  of  many  of  the  soluble  salts  of  the  metals  is 
astringent  or  acrid,  and  of  the  peculiar  kind  termed 
metallic. 

The  most  usual  colour  exhibited  by  the  metals  is  a  white, 
of  varying  shades.  It  is  nearly  pure  in  silver,  platinum, 
cadmium,  and  magnesium;  yellowish  in  tin  ;  bluish  in  zinc 
and  lead ;  grey  in  iron  and  arsenicum ;  and  is  reddish  in 
bismuth.  Calcium  is  pale  yellow,  gold  full  yellow ;  and 
copper  is  red. 


Metallic  A  Hoys.  20 1 

Many  of  the  metals  show  the  properties  of  malleability,  or 
the  power  of  being  flattened  under  the  hammer.  They  may 
also  be  extended  into  ribbon  or  foil,  by  passing  them  be- 
tween steel  rollers  :  among  these  are  gold,  silver,  platinum, 
palladium,  copper,  iron,  aluminum,  tin,  lead,  zinc,  and 
.thallium.  Gold  is  the  most  malleable  of  the  metals,  but 
silver  and  copper  may  also  be  hammered  into  very  thin 
leaves.  The  same  metals  are  likewise  ductile ;  that  is,  they 
admit  of  being  drawn  into  wire,  often  finer  than  a  hair,  by 
drawing  them  through  holes  in  a  hard  steel  plate,  termed  a 
draw-plate ;  the  holes  through  which  the  wire  is  made  to 
pass  being  successively  smaller  and  smaller. 

On  the  other  hand,  there  are  metals  so  brittle  that  they 
may  be  powdered  without  difficulty:  such  are  arsenicum, 
antimony,  and  bismuth.  These  metals  have  a  crystalline 
structure,  and  are  very  hard.  Metals  which  have  a  fibrous 
texture,  like  bar  iron,  are,  on  the  contrary,  very  tough. 

When  the  metals  are  combined  with  each  other,  the 
resulting  substance  is  called  an  alloy.  Many  of  these,  such 
as  brass,  German  silver,  bronze,  and  pewter,  are  used  largely 
in  the  arts,  on  account  of  advantages  which  they  offer  over 
their  constituent  metals  in  increased  hardness  and  elasticity, 
as  well  as  increased  fusibility.  Brass  is  a  hard,  somewhat 
fusible  alloy,  consisting  of  about  two-thirds  of  copper  and. 
one-third  of  zinc.  If  brass  be  melted  with  about  a  fifth  of 
its  weight  of  nickel,  it  furnishes  German  silver.  Bronze  is  an 
alloy  of  tin  and  copper,  of  which  there  are  several  varieties  : 
with  10  per  cent,  of  tin  it  forms  the  tough  gun-metal;  with 
20  per  cent,  of  tin  it  furnishes  the  sonorous,  elastic  bell- 
metal  ;  and  with  33  per  cent,  of  tin  the  hard,  white,  brittle 
metal  used  for  the  mirrors  of  telescopes. 

The  white  metal  used  in  types  for  printing  is  an  alloy  of 
about  i  part  of  antimony,  i  of  tin,  and  2  of  lead  ;  it  is 
fusible,  expands  on  becoming  solid,  so  as  to  fill  the  mould, 
and  is  hard  enough  to  bear  pressure,  but  will  not  cut  the 
paper,  All  the  alloys  melt  at  a  lower  temperature  than 


202  Native  Metals. 

that  which  would  be  the  mean  of  the  fusing  points  of  their 
components. 

Exp.  211. — Heat  in  a  small  iron  ladle  20  grams  of  lead  ;  as 
soon  as  it  is  melted  add  40  grams  of  bismuth  and  10  of  tin  ;.  they 
will  fuse  quickly,  and  an  alloy  will  be  thus  obtained  known  as 
fusible  metal\  it  melts  when  thrown  into  boiling  water,  although 
tin,  the  most  fusible  of  its  components,  does  not  melt  below 
228°  C. 

A  combination  of  a  metal  with  mercury  forms  an  amalgam. 
Some  amalgams  are  soft  and  semi-solid ;  others  are  brittle 
and  crystalline.  Alloys  and  amalgams  appear  to  consist  of 
definite  compounds,  which  are  often  mixed  with,  or  dissolved 
by,  an  excess  of  one  of  the  metals  employed ;  for  the  pro- 
portion of  the  metals  used  in  an  alloy  can  be  varied  within 
any  limits. 

Some  few  of  the  metals  are  found  in  the  native,  or  uncom- 
bined,  state  in  the  earth.  Among  these  the  most  important 
are  gold,  silver,  platinum  and  a  few  rare  metals  which 
accompany  it,  mercury,  bismuth,  and  copper.  M'ore  usually 
the  metals  occur  united  with  sulphur,  when  they  preserve 
their  metallic  brilliancy,  but  not  their  ductility  or  tenacity. 
Lead,  antimony,  mercury,  copper,  iron,  and  zinc  are  often, 
and  some  of  them  almost  always,  found  in  the  condition  of 
sulphides.  Other  metals — such,  for  instance,  as  tin,  iron, 
manganese,  and  chromium — are  met  with  as  oxides,  under  the 
aspect  of  dull  blackish  or  earthy  bodies.  The  metals  of  the 
earths,  and  of  the  alkalies,  are  generally  found  in  the  form  of 
salts,  such  as  sulphates,  carbonates,  silicates,  or  chlorides. 
Further  particulars  respecting  the  ores  of  the  metals,  their 
distribution  over  the  surface  of  the  earth,  the  formation  of 
mineral  veins,  and  the  methods  employed  for  extracting  the 
metals  for  use  in  the  arts,  will  be  found  in  the  text-book  on 
1  Metallurgy/ 

(44)  Classification  of  the  Metals. — The  metals  may  be 
divided  into  10  groups,  founded  upon  their  different  degrees 
of  attraction  for  oxygen,  and  the  properties  of  the  oxides 
which  they  form. 


Classification  of  the  Metals.  203 

Group  i:  5  Metals  of  the  Alkalies,  viz.  i.  Caesium;  2, 
Rubidium;  3.  Potassium  ;  4.  Sodium;  and  5.  Lithium,  with 
which  it  is  convenient  to  arrange  the  salts  of  ammonium, 
although  it  is  not  a  simple  body. — These  metals  are  monads, 
and  displace  i  atom  of  hydrogen  from  the  radicals  of  the 
acids.  They  are  soft,  easily  fusible,  and  volatile  at  high 
temperatures.  They  have  an  intense  attraction  for  oxygen, 
and  become  tarnished  as  soon  as  they  are  exposed  to  the 
air.  They  decompose  water  instantly  at  all  temperatures, 
with  rapid  disengagement  of  hydrogen,  and  form  a  soluble, 
powerfully  caustic  and  alkaline  compound,  which  may  be 
regarded  as  water  in  which  half  the  hydrogen  is  replaced  by 
metal.  They  form  but  one  set  of  salts  with  the  halogens. 
Though  they  furnish  but  a  single  chloride,  they  yield  several 
sulphides,  all  of  which  are  soluble.  When  exposed  to  the 
air  their  oxides  absorb  carbonic  acid  greedily,  and  form 
soluble  carbonates.  Only  two  of  them,  potassium  and 
sodium,  are  sufficiently  abundant  to  require  description. 
Caesium  and  rubidium  are  of  quite  recent  discovery,  and 
were  found  in  minute  quantity  in  the  water  of  a  mineral 
spring,  of  which  the  saline  residue  was  submitted  to  exami- 
nation by  the  method  of  spectrum  analysis,  lately  discovered, 
and  they  have  since  been  found  in  minute  quantity  in  the 
ash  of  various  plants,  and  in  some  crystallised  minerals. 

Group  2  :  3  Metals  of  the  Alkaline  Earths,  viz.  i.  Ba- 
rium ;  2.  Strontium ;  and  3.  Calcium. — These  are  dyads  ; 
they  displace  two  atoms  of  hydrogen  from  the  radicals  of  the 
acids.  When  thrown  into  water  they  decompose  it  with 
avidity,  and  set  hydrogen  free.  They  form  powerfully  basic 
oxides,  which  are  soluble  in  water,  though  lime  is  only 
sparingly  so.  These  oxides  absorb  carbonic  acid  rapidly, 
and  form  carbonates  which  are  insoluble  in  water,  but  some- 
what soluble  in  a  solution  of  carbonic  acid.  Their  phos- 
phates are  insoluble  in  water. 

Group  3  :  Metals  of  the  Earths. — The  only  one  of  prac- 
tical importance  is  i.  Aluminum  ;  but  2.  Glucinium ;  3. 


204  Classification  of  the  Metals. 

Yttrium ;  4.  Erbium ;  5.  Cerium  ;  6.  Lanthanium  ;  and  7. 
Didymium,  are  commonly  included  in  'this  division.  The 
last  six  are,  however,  very  rarely  met  with,  and  their  pro- 
perties are  only  imperfectly  known. 

Aluminum  is  a  triad :  it  forms  but  one  oxide ;  this  is 
insoluble  in  water,  and  is  but  feebly  basic. 

Group  4  :  4  Magnesian  Metals,  viz.  i.  Magnesium  ;  2. 
Zinc ;  3.  Cadmium  ;  4.  Indium. — These  metals  are  dyads  ; 
they  form  but  a  single  oxide,  which  is  insoluble  in  water. 
They  decompose  steam  at  a  red  heat,  but  are  without  action 
on  water  at  common  temperatures.  They  form  a  single 
soluble  chloride,  and  a  single  nearly  insoluble  sulphide. 

Group  5:  6  Metals  allied  to  Iron,  viz.  i.  Cobalt;  2. 
Nickel ;  3.  Uranium  ;  4.  Iron ;  5.  Chromium ;  and  6.  Man- 
ganese.— These  metals  are  remarkable  as  forming  two  sets 
of  compounds,  in  one  of  which  the  metal  is  dyad,  in  the 
other  triad.  They  furnish  several  oxides  :  those  which  con- 
tain least  oxygen  are  basic  and  insoluble ;  those  which 
contain  most  are  often  soluble,  and  are  then  distinctly  acid. 
Several  of  these  metals  are  magnetic  ;  they  are  oxidized  by 
passing  steam  over  them  when  heated  to  redness,  though 
they  do  not  decompose  water  at  ordinary  temperatures. 

Group  6 :  4  Metals  allied  to  Tin,  viz.  i.  Titanium ;  2. 
Tin  ;  3.  Zirconium;  and  4.  Thorinum.— They  are  all  tetrad, 
or  equivalent  to  4  atoms  of  hydrogen.  Tin  is  the  only 
one  of  practical  importance  :  it  furnishes  two  oxides,  both 
capable  of  acting  as  bases ;  but  the  higher  oxide  is  more 
often  acid. 

Group  7 :  2  Metals,  Molybdenum  and  Tungsten,  which  are 
hexad,  or  equivalent  to  6  atoms  of  hydrogen. — They  yield 
trioxides,  which  furnish  metallic  acids;  but  we  shall  not 
enter  into  any  description  of  them. 

Group  8  :  6  Metals.  They  present  in  their  combinations 
an  analogy  with  phosphorus,  viz.  i.  Niobium;  2.  Tantalum; 
3.  Vanadium ;  4.  Arsenicum ;  5.  Antimony ;  and  6.  Bismuth. 
— -They  furnish  at  least  two  oxides.  We  shall  not  enter  furthe 


Metals  of  the  Alkalies.  205 

into  any  description  of  the  first  three  of  these  metals,  but 
the  last  are  of  practical  importance. 

Group  9:  3  Metals,  viz.  i.  Copper;  2.  Lead;  and  3. 
Thallium,  which  are  not  closely  related. 

Group  10 :  9  noble  Metals,  viz.  i.  Mercury;  2.  Silver; 
3.  Gold ;  4.  Platinum,  with  which  are  associated  5  other  rare 
metals,  viz.  5.  Palladium;  6.  Rhodium;  7.  Ruthenium;  8. 
Osmium;  and  9.  Iridium,  which  we  need  not  further  notice. — 
The  first  four  metals  form  more  than  one  oxide,  but  have  so 
slight  a  tendency  to  union  with  oxygen  that  their  oxides  are 
decomposed  by  exposure  to  a  heat  below  redness.  All  the 
metals  of  this  group  are  commonly  found  in  the  native  state  ; 
but  mercury  and  silver  also  occur  as  sulphides.  Their  attrac- 
tions both  for  chlorine  and  for  sulphur  are  much  stronger 
than  for  oxygen.  Each  forms  more  than  one  chloride; 
their  compounds  have  a  tendency  to  combine  with  the 
chlorides  of  the  alkali-metals  to  form  double  salts. 

GROUP  I. — METALS  OF  THE  ALKALIES. 

i.  POTASSIUM.     2.  SODIUM.     3.  LITHIUM.    4.  CESIUM. 

5.  RUBIDIUM. — (AMMONIUM). 

(45)  POTASSIUM  :  Symb.  K;  Atom.  Wt.  39 ;  Sp.  Gr.  0*865  ; 
Fusing  Pt.  62-5°. 

This  metal  was  originally  obtained  by  decomposing  a 
fragment  of  caustic  potash  by  means  of  a  powerful  voltaic 
battery,  when  globules  of  potassium  were  separated  at  the 
negative  wire.  It  is  now  prepared  by  distilling  potassic 
carbonate  mixed  with  charcoal,  at  an  intense  heat,  in  iron 
bottles,  and  condensing  the  green  vapours  of  potassium  in 
receivers  containing  naphtha,  carbonic  oxide  being  dis- 
engaged during  the  process — 

K2CO3  +   2C     =     K2  +  3CO. 

This  is  a  difficult  and  dangerous  operation.  Potassium  vapour 
takes  fire  instantly  in  the  air  or  on  contact  with  water ;  it 
also  absorbs  carbonic  oxide,  and  the  compound  thus  formed, 
if  kept,  gradually  becomes  changed  into  a  black,  powerfully 


206  Potassium  Oxides  and  Hydrate. 

explosive  compound.  To  avoid  this  danger  potassium  is 
always  redistilled,  immediately  after  its  preparation,  in  a  small 
iron  retort  containing  naphtha  vapour. 

Potassium  is  a  brilliant  silver- white  metal,  soft  enough  to 
be  spread  with  a  knife.  It  tarnishes  immediately  that  it  is 
exposed  to  the  air,  and  decomposes  water,  evolving  hydro- 
gen as  soon  as  it  is  thrown  into  the  liquid.  (Exp.  30.)  The 
gas  takes  fire  from  the  heat  produced  by  the  action.  It  is 
necessary  to  preserve  the  metal  either  in  vessels  closed  so 
as  to  prevent  access  of  air,  or  under  some  liquid,  such  as 
naphtha,  which  contains  no  oxygen.  It  combines  imme- 
diately with  chlorine,  bromine,  iodine,  and  sulphur,  if  heated 
with  them. 

Potassium  furnishes  an  important  basic  oxide  (K2O), 
potash;  besides  this,  there  are  two  other  oxides  (K2O2  and 
K2O4),  which,  when  thrown  into  water,  give  off  oxygen,  and 
furnish  a  solution  of  potash.  The  anhydrous  potash  is 
difficult  to  obtain  pure,  and  is  seldom  prepared ;  but  its 
hydrate  is  a  very  important  substance,  and  is  known  as 
caustic  potash,  or  potassic  hydrate  (KHO).  This,  when 
dissolved  in  water,  furnishes  potash  ley.  It  is  prepared  by 
mixing  a  solution  of  potassic  carbonate  with  slaked  lime — 

K2CO3  +   CaO,  H2O     =     2KHO   +   CaCO3. 

If  the  solution  is  poured  off  from  the  calcic  carbonate  and 
evaporated  down  in  a  silver  dish,  an  intensely  caustic  solid 
substance  is  left,  which  fuses  at  a  red  heat,  and  may  be  cast 
into  metallic  moulds.  It  furnishes  the  hydrate  of  potash. 
This  substance  absorbs  both  moisture  and  carbonic  acid 
from  the  air.  Caustic  potash,  if  fused  in  glass  or  porcelain 
dishes,  corrodes  and  dissolves  them.  It  also  attacks  platinum 
vessels,  but  has  little  action  on  silver.  It  is  very  soluble 
both  in  water  and  in  alcohol.  The  solution  decomposes  the 
fats  and  oils,  and  converts  them  into  soluble  soaps.  Ordinary 
soft  soap  contains  potash  as  its  base.  Caustic  potash  is  also 
a  valuable  agent  in  the  laboratory,  where  it  is  used  for  the 


Salts  of  Potassium.  207 

purpose  of  absorbing  acid  gases,  such  as  the  carbonic.  In 
consequence  of  its  powerful  attraction  for  acids,  it  readily 
decomposes  the  salts  of  all  metals  which  form  oxides  in- 
soluble in  water,  and  it  precipitates  the  oxide  of  the  metal  in 
the  form  of  hydrate,  while  the  radical  of  the  acid  forms  a 
potassic  salt,  which  remains  in  solution ;  such  a  salt,  for 
example,  as  the  cupric  sulphate  is  decomposed  as  follows : — 

CuSO4  +   2KHO     =     K2SO4  +  CuO,  H2O. 

Potash  is  found  in  all  fertile  soils,  generally  in  the  clay 
derived  from  the  felspar,  which,  after  crumbling  down,  has 
become  mingled  with  other  substances.  Growing  plants 
require  potash  to  aid  in  forming  their  tissues.  The  alkaline 
salt  is  dissolved  by  the  rain-water  from  the  soil,  absorbed 
by  the  roots,  and  carried  by  the  circulation  of  the  sap  into 
the  plant,  where  it  becomes  combined  with  the  radical  of 
some  vegetable  acid.  When  the  plant  is  burned  the  salt 
of  the  vegetable  acid  is  decomposed,  and  the  potassium 
remains  in  the  ash,  chiefly  in  the  form  of  carbonate.  The 
more  soluble  portions  of  this  ash  are  washed  out  by  the 
action  of  water,  which  when  evaporated  leaves  the  potassic 
carbonate,  or  potash,  of  commerce,  which  is  imported  largely 
from  North  America  and  Russia.  Pearlash  is  the  first  pro- 
duce, refined  by  a  second  solution  in  a  very  small  quantity  of 
water,  and  evaporation  to  dryness. 

Potassic  chloride  has  also  been  found  native,  in  consider- 
able amount,  in  the  salt  beds  of  Stassfurth,  near  Magdeburg  ; 
and  it  is  present  in  sea  water  in  quantitv  sufficient  to  render 
this  a  very  important  source  of  supply. 

Potassium  forms  five  sulphides  :  K2S.  K2S2)  K2S3,  K2S4, 
and  K2S5.  They  are  all  soluble,  and  have  a  strongly  alkaline 
reaction.  When  mixed  with  an  acid,  they  all  give  off  sul- 
phuretted hydrogen,  and  also,  except  in  the  case  of  K2S, 
deposit  sulphur. 

Potassic  Carbonate  (K2CO3)  is  a  very  soluble  salt,  which, 
if  exposed  to  the  air,  attracts  moisture  from  it,  and  soon 


2o8  Nitre  or  Saltpetre. 

becomes  liquid.    It  is  strongly  alkaline,  and  restores  the  blue 
colour  of  red  litmus  paper. 

Exp.  2 1 2. — Burn  some  dry  brushwood ;  collect  the  ash,  and 
vvash  it  with  five  or  six  times  its  bulk  of  water.  Filter  off  from 
the  undissolved  substances.  Test  the  solution  with  a  piece  of 
reddened  litmus  paper,  which  will  at  once  become  blue.  Eva- 
porate the  solution  to  dryness  in  a  small  porcelain  dish.  If  the 
dry  mass  be  left  exposed  to  the  air  for  a  few  hours  it  will  become 
moist.  The  potassic  carbonate,  of  which  it  chiefly  consists, 
attracts  moisture  rapidly  and  deliquesces.  To  a  portion  of  the 
salt  add  a  few  drops  of  hydrochloric  acid :  brisk  effervescence 
occurs. 

Exp.  213. — Place  30  grams  of  pearlash  in  a  half-litre  bottle, 
and  dissolve  it  in  250  c.  c.  of  water.  Shake  20  grams  of  quick- 
lime with  five  or  six  times  its  bulk  of  boiling  water,  and  add  the 
pasty  mixture  (about  120  c.  c.  in  bulk)  to  the  solution  of  pearl- 
ash.  Agitate  the  mixture,  and  let  it  stand  till  it  is  clear.  Pour 
off  a  portion  of  the  liquid  :  it  is  a  solution  of  caustic  potash. 
Add  to  it  some  hydrochloric  acid  :  no  effervescence  will  occur. 
Agitate  a  tablespoonful  of  olive  oil  in  a  small  phial  with  3  or 
4  c.  c.  of  the  caustic  solution  diluted  with  ten  times  its  bulk 
of  water :  a  milky-looking  liquid  will  be  formed,  which  is  the 
first  stage  in  the  making  of  soap. 

Potassic  Hydric  Carbonate  (KHCO3). — If   a  current  of 
carbonic  acid  gas  be  passed  through  a  strong  solution  of 
potassic  carbonate,  it  is  quickly  absorbed,  and  crystals  of  a 
less  soluble  salt,  often  called  the  bicarbonate,  are  formed — 
K2CO3  +  CO2  +  H2O     =     2KHCO3. 

Potassic  Nitrate  (KNO3). — Another  important  salt,  usually 
called  nitre  or  saltpetre,  is  found  on  the  surface  of  the 
soil  in  some  parts  of  tropical  India.  It  is  also  obtained  in 
temperate  climates  by  allowing  animal  matter  mixed  with 
lime  rubbish  to  decay  in  heaps,  which  are  moistened  from 
time  to  time,  and  from  which  the  nitre  is  at  intervals  removed 
by  washing.  The  nitrogen  in  the  animal  refuse  become 
slowly  oxidized  into  nitric  acid,  and  this  combines  with  the 
lime  and  potash  present. 


Gunpowder.  209 

Nitre  has  a  cooling  saline  taste,  and  is  soluble  in  about 
3-|-  times  its  weight  of  cold  water. 

Exp.  214. — Dissolve  150  grams  of  nitre  in  a  quarter  of  a  litre 
of  boiling  water,  and  allow  it  to  cool  slowly :  six-sided  prisms 
of  nitre  will  crystallise  from  the  liquid. 

Exp.  21$. — Mix  a  portion  of  the  solution  with  three  or  four 
times  its  bulk  of  water,  and  dip  some  strips  of  filtering-paper 
into  the  liquid.  When  dry  the  paper,  called  touch  paper,  will 
smoulder  if  kindled. 

Exp.  216. — Throw  a  little  nitre  into  a  clear  fire  :  the  embers 
will  burn  with  brilliant  sparks. 

Exp.  217. — Put  a  few  dry  crystals  of  nitre  into  a  test-tube, 
and  heat  them  over  a  lamp :  they  will  melt  to  a  clear  liquid. 
Heat  them  more  strongly  :  they  will  be  decomposed,  gas  will 
escape,  which  will  rekindle  a  glowing  match,  and  which  at  first 
consists  of  pure  oxygen,  potassic  nitrite  being  formed — 
2KNO3  =  2KNO,  +  Oa. 

The  principal  use  of  nitre  depends  upon  this  readiness  to 
part  with  oxygen,  of  which  it  contains  nearly  48  per  cent., 
and  which  enables  it  to  add  great  intensity  to  combustion. 

Gunpowder  is  a  mechanical  mixture  of  about  75  parts  of 
nitre,  1 5  of  charcoal,  and  i  o  of  sulphur ;  the  quantities  of 
the  ingredients  used  being  nearly  in  the  proportions  of  i 
atom  of  sulphur,  2  of  nitre,  and  3  of  charcoal.  An  excess 
of  sulphur  is  to  be  avoided,  as  it  corrodes  the  gun.  The' 
application  of  a  spark,  or  even  of  a  temperature  of  about 
250°  C.,  produces  an  instantaneous  decomposition  of  the 
mixture,  attended  with  an  immense  production  of  gas  (chiefly 
carbonic  anhydride  and  nitrogen)  at  a  very  high  temperature, 
so  that  the  gases  at  the  moment  of  firing  become  expanded 
to  at  least  1500  times  the  bulk  of  the  gunpowder.  The 
chemical  change  is  sometimes  roughly  represented  as 
follows  : — 

S   +   3C   +   2KN03     =     3CO2  +   N2   -f   K2S; 
though  it  is  really  much  more  complex.     Gunpowder  thus 
contains  within  itself  the  oxygen  necessary  to  enable  it  to 
burn  in  a  space  excluded  from  air,  or  even  under  water ;  the 

p 


2io  Sodium  and  its  Compounds. 

oxygen  forming  either  carbonic  oxide  or  carbonic  anhydride/ 
while  nitrogen  is  set  free,  and  the  sulphur  remains  combined 
with  the  potassium. 

(46)  2.  SODIUM:  Symb.  Na;  Atomic  Wt.  23;  Sj>.  Gr. 
0-972  ;  Fusing  Pt.  97'6°. 

Sodium  much  resembles  potassium.  It  is  obtained  from 
its  carbonate,  by  heating  it  with  charcoal,  in  a  similar 
way  to  that  followed  with  potassium,  but  it  is  more  easily 
managed.  It  is  made  in  large  quantities  as  a  preparatory 
process  in  the  extraction  of  aluminum  and  magnesium. 
Sodium  gives  off  a  colourless  vapour,  which  burns  with  a 
bright  yellow  flame.  When  thrown  into  water  it  rises  to  the 
surface,  and  disengages  hydrogen  freely ;  but  the  gas  does 
not  generally  take  fire  unless  the  water  is  heated  first,  or  is 
small  in  quantity. 

Common  salt,  sodic  chloride  (NaCl),  is  the  great  source 
from  which  all  compounds  of  sodium  are  obtained.  This  is 
met  with  in  large  quantities  in  sea  water,  which  contains 
more  than  a  quarter  of  a  pound  in  a  gallon,  or  about  27 
parts  in  1000.  It  is  also  found  in  extensive  deposits  in 
Cheshire,  and  still  more  abundantly  in  the  mines  of  Wielitzka, 
in  Poland.  Sodium  is  also  found  in  Atacama  as  nitrate, 
and  in  many  rocks  and  minerals,  as,  for  instance,  in  soda 
felspar  or  albite,  and  in  cryolite  (sNaF,  A1F3),  a  fluoride  of 
sodium  and  aluminum. 

Sodium  forms  two  oxides,  Na2O  and  Na2O2.  The  first 
is  the  only  one  of  importance.  It  is  the  base  from  which 
the  salts  of  sodium  are  derived,  but  is  seldom  obtained  in  a 
pure  state. 

Caustic  Soda,  or  sodic  hydrate  (NaHO),  is  a  white  solid, 
very  soluble  in  water.  Caustic  soda  is  formed  on  a  large 
scale  in  the  alkali  works,  but  it  is  easily  prepared  by  treating 
a  solution  of  sodic  carbonate  with  slaked  lime,  in  a  manner 
similar  to  that  directed  for  obtaining  caustic  potash,  which  it 


Sodium  Salts.  211 

closely  resembles.  Soda  ley,  or  the  solution  of  this  hydrate 
in  water,  is  largely  used  in  the  manufacture  of  ordinary  ?hard 
soaps. 

Sodic  Chloride,  or  common  sea  salt  (NaCl),  is  often  ob- 
tained from  sea  water,  by  allowing  it  to  flow  into  very  shallow 
pools — constructed  for  the  purpose,  and  called  saltpans,  or 
salterns — where  the  water  evaporates,  and  becomes  concen- 
trated in  the  heat  of  the  sun.  The  salt  crystallises  out  in 
cubes,  and  forms  the  bay  salt  of  commerce.  The  mother 
liquor,  or  bittern,  retains  salts  of  potassium  and  magnesium, 
which  are  extracted  ;  and  it  also  furnishes  the  principal  source 
of  bromine.  In  some  inland  countries  brine  springs  furnish 
important  sources  of  supply  of  this  chloride.  Vast  beds  of 
rock  salt  also  occur  in  several  countries,  as  in  Galicia,  Canada, 
Spain,  and  in  several  parts  of  the  British  Islands,  especially 
in  Cheshire.  It  is  a  common  practice  where  coal  is  cheap  to 
allow  water  to  flow  down  into  the  bed  of  salt,  and  to  pump 
up  the  liquor  when  it  has  become  saturated.  The  brine  is 
then  boiled  down  and  crystallised.  Our  common  table  salt 
is  obtained  in  this  way. 

Sodic  chloride  in  small  quantities  is  essential  to  life.  It 
is  soluble  in  less  than  three  times  its  weight  of  water.  When 
heated  suddenly  it  decrepitates,  and  may  be  melted  at  a 
bright  red  heat.  Fish  and  meat  are  often  salted  to  preserve 
them  from  putrefaction ;  but  when  so  prepared  they  are 
much  less  nutritious  than  when  fresh,  as  the  salt  extracts  the 
nutritive  and  flavouring  juices,  which  become  saturated  with 
it  and  form  brine.  Salt  is  used  largely  as  a  manure  to  land. 
It  is  consumed  in  immense  quantities  in  the  alkali  works  for 
preparing  other  compounds  of  sodium ;  and  it  furnishes  the 
supply  of  chlorine  and  hydrochloric  acid. 

Sodic  Sulphate  (Na2SO4,  ioH2O)  was  formerly  known  as 
Glauber's  salt.  It  crystallises  in  four-sided  prisms,  which 
crumble  down  to  a  white  powder,  and  lose  their  water  when 
exposed  to  the  air.  It  is  very  soluble  in  water,  but  more  so 
at  33°  C.  than  either  at  a  higher  or  lower  temperature.  Salt 


212  Sodic  Carbonate. 

cake  is  the  name  given  to  the  sulphate  when  prepared  by 
decomposing  common  salt  in  a  furnace  with  sulphuric  acid, 
at  a  high  temperature,  as  a  preliminary  in  the  manufacture 
of  soda  ash.  Immense  volumes  of  hydrochloric  acid  gas 
are  then  given  off,  and  these  are  condensed  by  causing 
the  fumes  to  pass  through  large  towers  filled  with  broken 
coke  or  stone,  over  which  a  stream  of  water  is  kept  con- 
stantly trickling.  A  solution  of  hydrochloric  acid  is  thus 
obtained,  while  the  sodic  sulphate  is  left  in  the  furnace. 
The  decomposition  occurs  in  two  stages  ;  in  the  first,  one 
half  only  of  the  salt  is  decomposed,  hydric  sodic  sulphate 
being  formed,  and  the  first  half  of  the  hydrochloric  acid 
comes  off  easily.  The  expulsion  of  the  last  half  of  the  acid 
requires  a  higher  temperature,  and  is  driven  off  by  the  action 
of  the  fusible  hydric  sodic  sulphate  on  the  other  half  of  the 
sodic  chloride — 

(1)  NaCl   +   H3SO4         =     HC1   +   NaHSO4;  and 

(2)  NaCl   +    NaHSO4     =     HC1   +    Na2SO4. 

Sodic  Carbonate  (Na2CO3,  ioH2O).— This  salt  crystallises 
in  large  transparent  prisms,  which  effloresce  in  the  air.  It 
has  a  soapy  disagreeable  taste,  and  restores  the  blue  colour 
to  reddened  litmus  paper.  It  is  very  soluble  in  water  ;  and 
when  heated  melts  in  its  water  of  crystallisation,  which 
amounts  to  63  per  cent,  of  the  salt.  The  dried  residue  melts  at 
a  bright  red  heat.  The  dry  salt  is  made  in  enormous  quan- 
tities, and  sold  as  soda-ash,  which  is  used  in  the  manufacture 
of  glass,  in  soap-making,  in  cleansing  calicoes,  and  for  a  variety 
of  other  important  purposes.  In  order  to  prepare  this  carbo- 
nate, salt  cake  is  mixed  with  about  its  own  weight  of  chalk  and 
rather  more  than  half  its  weight  of  coal  dust.  This  material 
is  then  thrown  in  charges  of  about  125  kilog.  upon  the  floor 
of  a  hot  reverberatory  furnace  (Fig.  69),  divided  into  two 
beds  :  on  the  more  distant  bed  (B)  it  is  first  heated,  and  then 
thrust  on  to  the  bed  A,  nearest  the  fire  (c).  There  it  melts, 
and  gives  off  jets  of  gas,  which  take  fire,  and  bum  with  a 
yellow  flame.  As  soon  as  this  escape  of  gas  ceases,  the 


Manufacture  of  Soda. 


213 


mixture  is  raked  out  into  an  iron  trough,  the  next  charge 
is  pushed  down  to  the  lower  bed,  and  a  fresh  charge  is  in- 
troduced,    The  chemical  change  which  occurs  in  this  fusion 
Fig.  69. 


consists  mainly  :  ist,  in  reducing  the  sodic  sulphate  to  sul- 
phide, while  carbonic  oxide  is  formed  and  escapes,  taking 
fire,  and  becoming  converted  into  carbonic  anhydride — 

Na2SO4  +  40     =     Na2S  +  4CO. 

2nd.  The  sodic  sulphide  is  immediately  decomposed  by  the 
chalk  into  calcic  sulphide  and  sodic  carbonate — 

Na2S  +  CaCO3  =  Na2CO3  +  CaS. 
This  sodic  carbonate  is  always  mixed  in  the  process  with 
quicklime,  as  it  is  found  necessary  to  employ  chalk  in 
excess,  and  this  chalk  becomes  lime  in  the  high  temperature 
of  the  furnace.  A  certain  quantity  of  coal  is  also  always 
used  in  excess,  and  this  likewise  remains  mixed  in  the  fused 
mass,  technically  known  as  ball  soda  or  black  ash. 

This  ball  soda  is  now  broken  up,  and  placed  in  water  at 
about  45°  C.,  which  dissolves  out  the  sodic  carbonate,  but 
leaves  the  calcic  sulphide  undissolved.  This  undissolved 
residue  is  the  soda  waste,  so  troublesome  to  the  manufac- 
turers. The  solution  of  soda  is  next  evaporated  down,  and 
when  calcined  furnishes  the  soda-ash  or  crude  alkali  of 
commerce,  which  contains  from  50  to  56  per  cent,  of  caustic 
soda  (Na2O),  in  the  form  of  carbonate  and  hydrate.  If  this 
soda-ash  be  dissolved  in  water,  and  the  liquid  allowed  to 
cool  slowly  in  a  tank,  beautiful  transparent  crystals  of  the 
carbonate  (soda  crystals]  are  gradually  formed. 


2 14  Tests  for  the  A  Ikalies. 

Hydric  Sodic  Carbonate  (NaHCO3),  often  called  bicar- 
bonate, is  obtained  by  saturating  a  solution  of  the  carbonate 
with  carbonic  acid.  It  is  deposited  in  white  crystalline 
grains,  and  is  the  substance  commonly  used  for  producing 
an  effervescing  drink  with  lemon  juice. 

Tests  for  the  Alkali  Metals  in  Combination. — The  salts  of 
potassium  are  easily  distinguished  from  those  of  sodium. 

Exp.  218. — To  a  pretty  strong  solution  of  the  salt  in  question 
add  a  solution  of  tartaric  acid,  and  stir  the  mixture  with  a  glass 
rod  If  potassium  be  present,  white  gritty  crystals  of  cream  of 
tartar  (KHC4H4O6)  will  be  deposited,  but  no  such  precipitate 
will  occur  with  salts  of  sodium. 

Sodium  forms  salts  all  of  which  are  soluble  in  water,  so 
that  it  does  not  produce  any  precipitate  with  ordinary  test 
solutions.  It  also  gives  a  yellow  colour  to  a  colourless  flame, 
such  as  that  of  a  spirit  lamp  or  a  Bunsen  gas  burner,  whereas 
potassium  gives  a  violet-coloured  flame. 

The  alkalies  are  all  well  distinguished  from  each  other  by 
the  colour  which  they  give  to  flame,  especially  if  the  flame 
be  examined  by  means  of  the  spectroscope.  Potassium  is 
then  recognised  by  a  single  line  in  the  red  and  another  in 
the  violet ;  sodium,  by  a  pair  of  intense  lines,  so  close  that 
they  generally  seem  but  one,  in  the  yellow ;  lithium,  by  a 
single  intense  crimson  line,  and  sometimes  a  faint  one  in  the 
orange  if  the  flame  be  of  a  very  high  temperature ;  rubidium, 
by  two  lines  in  the  red  and  two  in  the  blue ;  and  caesium  by 
two  intense  lines  in  the  blue,  but  not  so  refrangible  as  those 
of  rubidium,  though  in  these  two  last-mentioned  spectra 
there  are  other  lines  of  less  importance. 

Potassium  salts  may  further  be  distinguished  from 
sodium  by  means  of  platinic  chloride,  which  forms  with  the 
chlorides  of  both  metals  a  double  salt ;  that  with  potassium 
(2KC1,  PtCl4)  is  nearly  insoluble,  that  with  sodium 
(2NaCl,  PtCl4,  4H2O)  crystallises  in  long  soluble  needles. 

Exp.  219. — Add  to  the  solution  of  two  or  three  decigrams  of 
potassium  chloride  in  a  small  porcelain  dish,  a  few  drops  of  hydro- 


A  mmonia. 


215 


chloric  acid^  then  an  excess  of  solution  of  platinic  chloride ; 
evaporate  to  dryness  over  a  saucepan  of  boiling  water,  arranged 
so  as  to  form  a  water-bath,  a  circular  disk  of  tin,  large  enough 
to  project  a  little  way  beyond  the  edge  of  the  saucepan,  being 
substituted  for  its  lid,  and  a  circular  hole  a  little  smaller  than 
the  dish  having  been  made  in  this  lid,  as  shown  in  Fig.  70* 
When  cold,  the  residue  is  to  be  re- 
dissolved  in  a  few  drops  of  water, 
which  will  remove  the  soluble  ma- 
terials, and  leave  the  sparingly  soluble 
salt  of  platinum  and  potassium  in 
small  octahedra. 

Caesium  and  rubidium  also  form 
similar  double  chlorides  with  pla- 
tinum chloride,  but  they  are  much 
less  soluble  in  hot  water  than  the 
potassium  salt,  a  difference  which  is 
sometimes  made  use  of  to  separate 
these  bases  from  potassium. 

(47)  3.  Ammonium  (H4N). — This 
is  not  a  metal,  nor  is  it  even  known 
in  a  separate  form  ;  but  it  is 
generally  considered  to  be  the  com- 
pound quasi  metal  contained  in  the  salts  formed  by  the 
action  of  the  volatile  alkali  ammonia  on  the  acids  :  such,  for' 
instance,  as  sal  ammoniac,  the  compound  obtained  by 
neutralising  hydrochloric  acid  with  ammonia ;  ammonic 
nitrate,  the  salt  obtained  by  neutralising  nitric  acid  with 
ammonia;  and  ammonic  sulphate,  the  salt  obtained  by 
neutralising  oil  of  vitriol  with  ammonia.  All  these  salts 
crystallise  in  the  same  form  as  the  corresponding  salts  of 
potassium  with  the  same  acids,  and  in  every  case  the 
quantity  of  hydrogen  present  in  the  salt  formed  from  am- 
monia is  sufficient  to  convert  it  into  the  body  ammonium, 
which  seems  to  act  as  a  compound  metal,  much  in  the  same 
way  as  cyanogen  is  found  to  act  like  a  compound  halogen. 
For  instance  : — 


2 1 6  Carbonate  of  A  mmonia. 

Ammonia  Ammonium          Corresponding  to 

Salt  Salt  Potassium  Salt 

Hydrochlorate  H3N,  HC1  =     (H4N)C1  (K)C1 

Nitrate  H3N,  HNO3        =    (H4N)NO3          (K)NO3 

Sulphate          (H3N),,  H,SO4     =    (H4N),SO4         (K)2SO4 

A  solution  of  ammonia  in  water  may,  in  fact,  be  regarded 
•is  ammonium  hydrate,  the  analogous  compound  to  potas- 
sium hydrate — 

HNO3  +   (K)HO     =     (K)NO3  +  H2O. 

Upon  this  supposition  it  is  easy  to  explain  the  diverse 
position  of  a  metallic  salt  and  the  separation  of  the  oxide,  on 
adding  to  it  a  solution  of  ammonia ;  as,  for  instance  : — 

FeaCl6   +   6[(H4N)HO]     =     FeaO3,  sHaO    +   6[(H4N)C1] 
FeaCl6   +   6[(K)HO]    "      -     Fe2O3,  3HaO   +   6[(K)C1]. 

Exp.  220. — Dissolve  a  piece  of  sodium  of  the  size  of  a  pea, 
in  about  2  cub.  cm.  of  pure  mercury,  in  a  test-tube  :  the  two 
metals  unite  suddenly  with  flame.  When  cold,  pour  the  amalgam 
into  a  large  watch-glass,  and  cover  it  with  a  saturated  solution 
of  sal  ammoniac  :  the  amalgam  will  gradually  swell  up  and 
become  pasty,  and  will  often  float  when  thrown  into  water. 

This  at  one  time  was  held  to  be  an  amalgam  of  ammonium 
[(NH4)2Hg]  dissolved  in  excess  of  mercury,  but  there  is  little 
doubt  that  it  is  simply  mercury  distended  by  hydrogen  and 
ammonia  gases,  its  bulk  having  been  found  to  vary  accord- 
ing to  the  pressure  upon  it — 

2NH4C1   +   Na2Hg    =    2NH3  +  H2  +   2NaCl  +  Hg. 

It  gives  off  hydrogen  and  ammonia  on  standing,  and  also 
when  thrown  into  water. 

One  of  the  most  remarkable  of  the  salts  of  ammonium  is  the 
common  smelling-salt,  or  sesquicarbonate  2[(H4N)2O],  3CO2, 
which  is  obtained  by  heating  a  mixture  of  chalk  with  half 
its  weight  of  powdered  sal  ammoniac,  and  subliming  it 
gradually — 

6H4NC1   +   3CaCO3 
=   SCaCl,   +   2[(H4N)aO],sCO,   +    2H3N    +    H3O. 

A  large  quantity  of  free  ammonia  escapes  in  the  operation, 


Baryta.  217 

and  the  salt  is  always  losing  carbonate  of  ammonia,  which 
causes  its  pungent  smell ;  and  a  white  powder,  the  bicarbon- 
ate, or  hydric  ammonic  carbonate,  is  left,  2[(H4N)2O],  3CO2 
becoming  2H4NHCO3  +  (H3N)2CO2. 

A  solution  of  sal  ammoniac  gives  a  yellow  nearly  insoluble 
double  salt  with  platinic  chloride  (2H4NC1,  PtCl4),  which 
crystallises  in  cubes  or  octahedra,  like  the  potassium  salt.  It 
is  often  used  for  ascertaining  the  quantity  of  an  ammonium 
salt  in  solution.  A  still  more  delicate  test  is  that  known  as 
Nessler's,*  which  gives  a  brown  stain  when  the  solution 
contains  less  than  a  millionth  of  its  weight  of  a  salt  of 
ammonium. 

GROUP  II. — METALS  OF  THE  ALKALINE  EARTHS. 
i.  BARIUM.     2.  STRONTIUM.     3.  CALCIUM. 

(48)  i.  BARIUM  :  Symb.  Ba;  Atomic  Wt.  137. 

This  metal  is  scarcely  known  in  a  separate  state.  When 
combined  with  oxygen,  it  forms  Baryta  (BaO),  and  a  dioxide 
(BaO2).  Baryta  (BaO)  may  be  obtained  by  treating  baric 
nitrate  in  a  crucible  till  the  salt,  which  decrepitates  and 
melts,  again  becomes  solid,  and  finally  ceases  to  give  oif 
oxygen  at  a  bright  red  heat.  The  baryta  is  left  as  a  grey 
porous  mass,  which  absorbs  moisture  and  carbonic  acid 
from  the  air.  If  mixed  with  half  its  weight  of  water  it  slakes, 
forming  a  hydrate,  whilst  great  heat  is  given  out.  This 
hydrate  is  largely  soluble  in  boiling  water,  and  the  solution 
deposits  a  crystalline  hydrate  of  baryta  as  it  cools.  The 
liquid  is  strongly  alkaline,  and  becomes  milky  by  the  action 
of  carbonic  acid. 

The  dioxide  (BaO2)  may  be  formed  by  passing  oxygen 

*  Nessler's  test  for  ammonia  is  prepared  thus :  add  to  a  solution  of 
mercuric  chloride  a  solution  of  potassic  iodide  till  the  red  precipitate 
first  formed  is  nearly  all  dissolved.  Then  add  a  large  excess  of  caustic 
potash ;  let  the  mixture  stand  in  a  stoppered  bottle  for  three  or  four 
days,  and  decant  when  clear.  It  gives  a  brown  precipitate  when  added 
to  a  solution  containing  a  salt  of  ammonium.  This  consists  of  HgH^NI. 


2 1 8  Salts  of  Barium. 

over  anhydrous  baryta  at  a  low  red  heat ;  but  if  the  heat  be 
raised  to  full  redness,  the  second  atom  of  oxygen  is  given  off 
again,  and  baryta  is  reproduced.  If  this  oxide  be  dissolved 
at  a  low  temperature  in  hydrochloric  acid,  baric  chloride  is 
formed,  and  the  remarkable  body  H2O2,  hydrogen  peroxide, 
is  formed  in  the  liquid — 

BaO2  +   2HC1     ==     BaCl2  +   H2O2. 

The  most  abundant  compounds  of  baryta  are  the  sulphate 
and  the  carbonate. 

The  sulphate  (BaSO4)  is  a  very  heavy  mineral,  sp.  gr.  4*6, 
the  name  baryta  having  been  given  to  the  earth  in  allusion 
to  its  weight,  from  fiapvc,  '  heavy.'  It  is  found  crystallised 
in  right  rhombic  prisms.  It  is  insoluble  in  water  and  in 
solutions  of  the  acids.  It  is  easily  obtained  artificially  by 
mixing  a  solution  of  a  sulphate  with  one  of  baric  chloride, 
or  any  soluble  barium  salt.  This  sulphate,  although  in- 
soluble, furnishes  a  sulphide  soluble  in  dilute  acids  if  it  be 
heated  with  carbon. 

Exp.  221. — Grind  about  10  grams  of  the  sulphate  to  a  very 
fine  powder ;  mix  it  with  an  equal  weight  of  flour,  and  make  it 
into  a  paste  with  oil;  place  this  mixture  in  a  crucible,  with  a 
little  charcoal ;  lute  on  the  cover  of  the  crucible  with  fireclay, 
and  when  the  lid  is  dry  raise  the  crucible  gradually  to  an  intense 
heat  in  a  furnace,  keeping  it  up  for  about  an  hour  :  then  allow 
it  to  cool. 

In  this  process  the  sulphate  becomes  reduced  to  sulphide, 
while  carbonic  oxide  escapes — 

BaSO4  +  4C     =     BaS   +  4CO. 

Exp.  222. — Treat  the  residue,  when  cold,  with  a  large  quantity 
of  boiling  water.  Everything  should  dissolve  except  the  excess 
of  carbon. 

The  sulphide  thus  obtained,  if  treated  with  hydrochloric 
acid,  is  dissolved,  baric  chloride  is  formed,  and  sulphuretted 
hydrogen  escapes — 

BaS  +   2HC1     =     BaCl2  +  H2S. 


Compounds  of  Calcium.  2 19 

This  chloride  is  one  of  the  salts  most  often  used  for  pre- 
cipitating sulphuric  acid  from  the  sulphates.  Baric  Car- 
bonate (BaCO3)  forms  the  mineral  called  Witherite,  found 
occasionally  in  the  lead  veins  in  the  north  of  England.  It 
is  insoluble  in  water;  soluble  with  effervescence  in  dilute 
acids ;  and  is  easily  obtained  in  the  form  of  a  white  powder 
by  mixing  a  solution  of  sodic  carbonate  with  one  of  baric 
chloride  or  nitrate. 

This  carbonate,  and  all  the  soluble  barium  salts,  are 
strongly  poisonous,  the  best  antidote  being  Epsom  salts. 

Tests  for  Barium  Salts. — The  best  test  for  the  barium 
salts  in  solution  is  the  formation  of  a  white  precipitate,  in- 
soluble in  nitric  acid,  on  adding  a  solution  of  calcic  sulphate. 
They  communicate  a  green  tinge  to  flame,  and  form,  with 
a  solution  of  sodic  hyposulphite,  a  white  sparingly  soluble 
hyposulphite.  This  last  test  is  useful  as  a  means  of  dis- 
tinguishing them  from  strontium  salts,  which,  however,  give 
a  crimson  colour  to  flame. 

2.  STRONTIUM:   Symb.  Sr;   Atomic  Wt.  87-5;   Sp.   Gr. 

2'54- 

This  metal  occurs  chiefly  combined  as  sulphate  and 
carbonate  in  forms  resembling  the  same  compounds  of 
barium,  for  which  it  was  long  mistaken  j  but  its  compounds 
are  much  less  abundant.  Its  salts  are  not  poisonous.  The 
nitrate  is  used  to  give  a  red  fire  in  the  manufacture  of 
fireworks.  Strontic  sulphate  is  rather  more  soluble  than 
baric  sulphate. 

(49)  3.  CALCIUM:  Symb.  Ca;  Atomic  Wt.  40;  Sp.  Gr. 
1*578. 

This  is  a  malleable  metal  of  a  very  pale  yellow  colour. 
It  is  seldom  prepared,  but  may  be  procured  by  decomposing 
its  fused  chloride  by  the  voltaic  battery.  Calcium  tarnishes 
quickly  when  exposed  to  the  air.  It  forms  but  a  single 
oxide  (CaO),  the  very  important  substance  known  as  lime, 
which  is  extremely  abundant,  both  as  carbonate  and  as 


22O  Limestone. 

sulphate;  the  chalk  and  limestone  rocks,  as  well  as  the 
different  forms  of  marble,  all  consist  of  carbonate  more  or 
less  pure.  Compounds  of  calcium  are  also  found  in  all 
fertile  soils,  and  they  occur  in  a  large  number  of  crystallised 
minerals,  amongst  which  fluor  spar,  calcic  fluoride,  is  one  of 
the  most  important. 

Calcic   Oxide.— Lime  (CaO) :    Atomic  Wt.  56.— This   is 
obtained  by  heating  the  pure  carbonate  for  some  time  to 
bright  redness,  carbonic  anhydride  being  expelled — 
CaCO3     =     CaO  +  CO2. 

Exp.  223. — Place  a  few  lumps  of  black  marble  in  the  open 
fire,  or  in  an  open  crucible,  with  a  hole  at  the  bottom,  and  heat 
it  strongly  for  an  hour  or  two.  When  it  is  completely  con- 
verted into  quicklime,  the  lumps,  when  broken  across,  will  be 
quite  white. 

Common  lime  is  made  by  heating  limestone  for  some 
days  in  a  large  egg-shaped  or  conical  kiln,  in  which  a  fire  is 
kindled  at  the  bottom. 

Freshly  burnt  lime  is  called  quicklime.  It  is  a  white  in- 
fusible substance,  and  if  left  exposed  to  the  air  it  swells  up 
gradually  and  falls  to  powder.  If  water  be  poured  upon  it 
great  heat  is  given  out,  the  earth  swells  up  and  combines 
with  part  of  the  water,  and  is  said  to  become  slaked.  In 
this  process  a  definite  hydrate  (CaO,  H2O)  is  formed  :  it  is 
a  light  dry  powder,  from  which  the  water  may  be  driven 
out  at  a  red  heat. 

Lime  is  sparingly  soluble  in  water;  the  solution  forms 
limewater,  which  is  alkaline,  and  is  often  used  as  a  test  for 
the  presence  of  carbonic  acid,  by  which  it  is  immediately 
rendered  turbid. 

Milk  of  lime  is  merely  slaked  lime  diffused  through  water. 

The  great  consumption  of  lime  is  in  mortars  and  cements. 
Common  mortar  is  made  by  mixing  i  part  of  lime  into  a 
thin  paste  with  water,  and  adding  3  or  4  parts  of  sharp  sand. 
It  hardens  slowly  in  the  air,  and  gradually  absorbs  carbonic 
acid. 


Plastey  of  Paris.  221 

Limestones  are  rocks  originally  deposited  in  the  form  of 
mud  from  water,  and  vary  in  composition,  sometimes  being 
mixed  with  clay,  sometimes  with  sand,  or  with  other 
materials  which  alter  their  properties  when  burned.  Com- 
mon mortar  is  gradually  dissolved  away  by  the  action  of 
water,  but  when  the  limestone  contains  clay  in  moderate 
quantity  it  furnishes,  after  burning,  a  cement  which  hardens 
under  water.  Such  lime  is  called  hydraulic  lime.  It  slakes 
much  more  slowly  than  pure  lime. 

Lime  is  moreover  largely  used  as  a  manure,  being  especially 
useful  in  reclaiming  peat  or  bog  land,  where  it  decomposes 
the  excess  of  vegetable  matter  and  renders  the  soil  more 
open,  while  the  lime  becomes  a  carbonate. 

Lime  is  used  also  in  many  chemical  processes,  as  in  con- 
verting the  carbonate  of  potassium  and  sodium  into  caustic 
alkalies.  It  is  used  by  the  tanner  to  loosen  the  hair  on 
hides  by  dissolving  the  outer  surface  of  the  skin,  and  it  is 
employed  to  remove  impurities  from  coal  gas. 

Calcic  Chloride  (CaCl2)  is  made  by  dissolving  limestone  or 
chalk  in  diluted  hydrochloric  acid,  and  evaporating  the 
solution.  It  may  be  obtained  in  deliquescent  crystals  with 
6H2O  j  but  when  strongly  heated  it  loses  4H2O,  and  leaves 
a  porous  mass  still  retaining  2H2O,  which  absorbs  moisture 
greedily,  and  is  often  used  for  drying  gases,  which  are  allowed 
to  pass  slowly  over  it. 

Calcic  Sulphate,  or  gypsum  (CaSO4,  2H2O),  is  an  abundant 
and  important  mineral.  When  heated  to  about  500°  it  loses 
its  water,  and  crumbles  down  to  a  white  powder,  which  is  ex- 
tensively used  for  finishing  the  interior  of  houses,  under  the 
name  of  plaster  of  Paris.  If  the  dry  powder  be  made  into 
a  thin  paste  with  water,  the  mixture  becomes  solid  in  a  few 
minutes,  owing  to  the  recombination  of  the  water  with  the 
sulphate,  and  expands  slightly,  eventually  becoming  as  hard 
as  the  original  gypsum.  If  the  gypsum  has  been  heated 
to  redness  it  loses  its  porosity,  and  no  longer  *  sets '  with 
water. 


222  Calcic  Carbonates. 

Exp.  224. — Select  a  medal  suitable  for  the  purpose ;  paste  a 
shallow  rim  of  paper  round  it,  so  as  to  make  it  like  the  lid  of  a 
pill-box,  and  anoint  the  surface  of  the  medal  very  lightly  with  oil. 
Mix  a  little  of  the  dry  plaster  with  water  till  it  becomes  of  the 
consistence  of  thin  cream ;  apply  it  carefully  with  a  hair  pencil  to 
every  part  of  the  surface,  so  as  to  exclude  air  bubbles  ;  then  pour 
a  thicker  mixture  into  the  mould.  Allow  it  to  remain  for  an 
hour.  The  cast  may  then  be  removed  :  it  will  be  a  reversed 
copy  of  the  medal 

Gypsum  in  certain  cases  forms  a  valuable  manure  Calcic 
sulphate  is  a  common  impurity  in  spring  waters. 

Calcic  Carbonate  (CaCO3  :  Atomic  Wt.  100). — Besides  its 
occurrence  in  marble  and  in  Iceland  spar,  which  crystallises 
in  rhombohedra,  this  carbonate  is  found  in  crystals  of  a 
different  system,  the  prismatic,  forming  the  mineral  arago- 
nite.  It  forms  the  different  varieties  of  limestone,  chalk, 
oolite,  and  calcareous  marl,  and  is  the  principal  constituent 
of  corals,  of  the  shells  of  fish,  and  of  egg-shells,  besides  enter- 
ing into  the  composition  of  the  bones  of  animals  in  greater 
or  less  amount.  It  also  forms  a  combination  with  magnesic 
carbonate,  which  is  known  as  dolomite  or  magnesian  lime- 
stone, which  is  very  abundant  in  certain  geological  deposits. 
Many  of  these  compact  limestone  rocks  are  highly  prized 
for  building.  Portland  stone  is  an  oolite ;  that  is,  it  is  formed 
of  little  rounded  grains,  which  resemble  the  hard  roe  of  a  fish 
in  aspect. 

Calcic  carbonate  is  scarcely  soluble  in  pure  water,  but  it 
is  freely  dissolved  by  water  containing  carbonic  acid,  and  is 
deposited  again  in  crystals  as  the  gas  escapes.  Enormous 
masses  of  the  crystallised  carbonate  are  thus  formed  in  the 
•lapse  of  ages.  In  the  limestone  hills  of  Derbyshire  and 
other  places,  caverns  occur  where  this  process  is  always  going 
on ;  water  charged  with  carbonic  acid  and  calcic  carbonate 
makes  its  way  through  the  roof  of  the  cavern,  where,  as  the 
carbonic  acid  gradually  escapes,  the  carbonate  is  deposited 
in  hanging  columns,  like  icicles,  termed  stalactites,  whilst  the 
water  falling  upon  the  floor  deposits  a  fresh  portion  of  the 


Aluminum.  223 

dissolved  carbonate,  which  slowly  grows  upwards  till  the 
stalagmite  so  formed  meets  the  stalactite  depending  from  the 
roof,  and  thus  a  natural  pillar  of  crystallised  calcic  carbonate 
is  formed. 

In  volcanic  districts,  where  the  springs  are  often  highly 
charged  with  carbonic  acid,  this  deposition  is  often  very 
rapid;  the  spring,  as  it  escapes,  deposits  a  porous  material 
termed  tufa,  while  upon  sides  of  the  stream  a  more  compact 
substance,  known  as  travertine,  which  is  a  sort  of  marble 
highly  prized  for  building  purposes,  is  formed. 

Tests  for  Calcium  Salts. — Solutions  of  these  salts  give  no 
precipitate  with  ammonia,  or  with  ammonic  sulphide,  but 
they  give  a  white  one  of  calcic  carbonate  with  sodic  or  po- 
tassic  carbonate,  as  do  also  the  salts  of  barium,  and  of  stron- 
tium ;  from  these  they  may  be  distinguished  by  means  of  a 
solution  of  calcic  sulphate,  with  which  calcium  salts  give  no 
precipitate.  Ammonia  oxalate  gives,  in  neutral  or  alkaline 
solutions  of  calcium  salts,  a  white  precipitate  of  calcic 
oxalate,  soluble  in  nitric  or  hydrochloric  acid,  but  not  in 
acetic  acid.  They  give  a  greenish  yellow  tinge  to  flame. 


CHAPTER  XII. 
GROUP  III. — METALS  OF  THE  EARTHS. 

(50)  i.  ALUMINUM  :  Symb.  Al ;  Atomic  Wt.  27-5  ;  Sf. 
/>.  2-67. 

This  metal  derives  its  name  from  alum,  of  which  material 
it  constitutes  between  5  and  6  per  cent.  Its  compounds 
are  among  the  most  abundant  constituents  of  the  rocks, 
including  felspar,  hornblende,  and  slate.  Aluminum  may  be 
obtained  from  cryolite  (sNaF,  A1F3)  by  fusing  it  with  sodium ; 
but  the  method  usually  practised  consists  in  decomposing 
sodic  aluminic  chloride  (NaCl,  A1C13)  by  heating  it  with 


224  Calico  Printing. 

sodium  ;  an  intense  action  occurs,  and  the  aluminum  is  ob- 
tained in  a  melted  state  under  the  fused  sodic  chloride — 
NaClAlCl3  +   3Na      =     4NaCl  +  AL 

Aluminum  is  a  white  malleable  metal,  resembling  zinc  in 
colour  and  hardness.  It  may  be  rolled  into  foil,  and  drawn 
into  wire.  When  struck,  it  gives  a  clear  musical  sound.  It 
melts  at  a  temperature  below  that  needed  for  the  fusion 
of  silver.  It  preserves  its  brightness  in  the  air,  and  is  but 
slowly  oxidized  at  a  red  heat.  Nitric  acid  attacks  it  with 
difficulty,  but  it  is  rapidly  dissolved  by  hydrochloric  acid, 
and  by  solutions  of  the  alkalies,  hydrogen  being  given  off. 
This  metal,  with  about  90  per  cent,  of  copper,  forms  a  golden 
yellow  alloy,  called  aluminum  bronze,  well  fitted  for  castings. 

Alumina  (A12O3). — There  is  only  one  oxide  of  this  metal, 
the  earth  alumina,  which,  when  crystallised,  constitutes  the 
Oriental  ruby,  the  sapphire,  and  corundum.  Emery  is  an- 
other form,  of  less  purity.  All  these  minerals  are  very  hard ; 
their  colour  is  due  to  small  quantities  of  the  oxides  of  chro- 
mium, iron,  or  manganese.  Alumina,  combined  with  silica, 
forms  the  different  varieties  of  clay,  and  is  the  basis  of  porce- 
lain and  earthenware.  The  soluble  salts  of  alumina  are 
of  value  to  the  calico  printer.  Hydrated  alumina  combines 
intimately  with  many  vegetable  colours,  and  forms  with  them 
pigments,  called  lakes. 

Exp.  225. — Grind  some  madder  root  into  a  coarse  powder, 
and  pour  a  litre  of  boiling  water  upon  three  or  four  grams  of 
it.  Stir  it  up  occasionally;  then  let  it  settle  for  three  or  four 
hours  ;  pour  off  the  red  liquor.  Mix  it  with  a  solution  of  4  grams 
of  alum,  and  add  a  solution  of  4  grams  of  sodic  carbonate.  Let 
the  solution  rest  in  a  tall  glass  jar  :  a  red  deposit  or  lake,  con- 
sisting of  the  colouring  matter  combined  with  the  alumina,  will 
be  produced. 

If  a  pattern  be  stamped  on  calico  with  a  solution  of  alum, 
and  be  then  boiled  with  a  solution  of  madder,  the  figures  will 
be  permanently  dyed,  while  the  colour  may  be  easily  washed 
out  of  the  remainder  of  the  cloth.  In  this  case  the  alumina 


Alumina.  225 

in  the  alum  fixes  itself  upon  the  cloth,  and  acts  as  a  mordant, 
which  '  bites  in '  the  colour,  or  attaches  it  to  itself,  and  thus 
renders  the  dye  fast.  Other  oxides,  such  as  those  of  iron, 
chromium,  and  tin,  are  used  for  the  same  purpose,  but  they 
change  the  colour  of  the  dye  stuff  at  the  same  time  that  they 
fix  it  upon  the  calico.  All  metallic  oxides  used  for  such  a 
purpose  are  termed  mordants  by  the  dyer. 

Alumina  may  be  precipitated  from  its  salts  by  a  solution 
of  potash,  but  an  excess  of  potash  redissolves  the  precipitate. 
Ammonia  also  precipitates  the  alumina  as  a  bulky  jelly-like 
hydrate,  but  does  not  redissolve  it. 

This  hydrate  is  freely  soluble  in  diluted  acids,  but  the  solu- 
tion has  the  property  of  reddening  litmus  ;  so  that,  while  the 
hydrate  acts  the  part  of  a  feeble  acid  towards  potash  and  soda, 
which  dissolve  it,  it  also  acts  the  part  of  a  base  towards  acids, 
though  it  is  but  a  weak  base,  compared  with  either  potash 
or  soda,  or  bases  which  contain,  like  them,  i  atom  of  oxygen 
with  2  atoms  of  a  monad,  or,  like  calcium,  i  atom  of  a  dyad 
metal.  Alumina  resembles  ferric  and  chromic  oxides.  It 
crystallises  when  united  with  acids  in  the  same  form  as  these 
oxides  do  when  acted  upon  by  the  same  acids,  and  con- 
sequently it  is  regarded  as  a  sesquioxide. 

The  different  basic  oxides  may  be  compared  together  in 
this  manner  : — 


MONOXIDES 

Monads  Dyads 

KaO  Potassic  Oxide    CaO  Calcic  Oxide 
Na,O  Sodic  Oxide         FeO  Ferrous  Oxide 


SESQUIOXIDES 


FezO3  Ferric  Oxide 


AgzO  Argentic  Oxide  CrO  Chromous  Oxide 

Alumina  forms  a  yellow  chloride  (A12C16),  which  is  vola- 
tile below  a  red  heat.  It  is  obtained  by  mixing  alumina 
and  powdered  charcoal  into  a  paste  with  oil,  heating  the 
ture  to  redness,  and  sending  a  current  of  dry  chlorine 
gas  over  it :  the  chlorine  unites  with  aluminum,  and  the 
carbon  with  the  oxygen — 

A1203  +  sC  +  3C12     =     A12C16  +  3CO. 
The  chloride  is  used  in  extracting  the  metal. 

Q 


226  Alums. 

But  the  most  important  salt  is  the  sulphate,  which  is 
obtained  by  treating  clay  for  some  days  with  sulphuric  acid, 
at  a  heat  nearly  sufficient  to  make  the  acid  boil.  This  sul- 
phate (A123SO4)  is  very  soluble ;  but  if  mixed  with  a  due  pro- 
portion of  potassic  sulphate,  it  forms  a  salt,  which  crystallises 
in  fine  octahedra,  and  is  well  known  as  potassium  alum 
(KA12SO4,  i2H2O). 

Alum  is  a  double  salt,  which  is  made  in  vast  quantities 
for  the  use  of  the  calico  printer.  Ammonic  sulphate  is  now 
largely  employed  instead  of  the  potassic  salt.  It  then  pro- 
duces ammonium  alum  (H4N,  Al2SO4,  i2H2O),  which  crys- 
tallises quite  as  readily  and  in  exactly  the  same  form  as 
the  potassium  salt.  The  place  of  the  aluminic  sulphate 
may  be  supplied  by  ferric  sulphate,  chromic  sulphate,  and 
manganic  sulphate.  In  each  case  a  salt  is  formed,  which  is 
different  in  colour  from  true  alum,  but  like  it,  and  crystallises 
in  octahedra,  resembling  those  of  alum ;  so  that  there  are  a 
number  of  alums  known,  some  of  which  may  be  represented 
as  follows  : — 

Ammonium  Alum      .        .     (H4N)Al2SO4,  i2HaO 
Potassium  Alum        .        .  KAbSO4,  i2HaO 

Iron  Alum          .        .        .  KFe2SO4,  I2H,O 

Manganese  Alum       .        .  KMn2SO4,  i2H2O 

Chrome  Alum    .        .        .  KCr2SO4,  I2H,O 

Alum  has  a  sweetish,  astringent  taste.  Its  solution  reddens 
litmus  strongly.  When  heated  it  melts,  first  in  its  water  of 
crystallisation,  then  it  froths  up,  forms  a  tenacious  paste, 
and  at  last  becomes  a  white,  bulky,  porous,  infusible  mass, 
called  burnt  alum. 

A  good  deal  of  alum  is  made  by  roasting  alum  schist  (a 
kind  of  black  bituminous  clay,  which  contains  a  good  deal  of 
pyrites)  for  some  weeks  at  a  low  temperature.  The  pyrites 
absorbs  oxygen,  and  becomes  gradually  converted  into  ferrous 
sulphate,  while  the  second  atom  of  sulphur  in  the  pyrites 
combines  with  oxygen,  and  the  product  unites  with  alumina, 
forming  a  mixture  of  aluminic  and  ferrous  sulphates — 
2FeS2  +  ;O2  =  2FeSO4  -f 


Clays — Varieties  of  Felspar.  227 

and  on  adding  potassic  chloride,  alum  crystallises  out  from 
the  mixed  sulphate  and  chloride  of  iron — 

FeSO4  +  A123SO4  +  2KC1  =  FeCl2  4-  2KA12SO4. 

Silicates  of  Alumina — Clays. — Alumina  forms  a  great 
number  of  silicates.  All  the  varieties  of  clay  consist  of 
aluminic  silicate,  more  or  less  mixed  with  other  matters 
derived  from  the  rocks  which,  as  they  have  crumbled  down, 
have  furnished  the  clay.  The  best  fire  clay  consists  of 
Al2O32SiO2,  2H2O.  It  is  used  in  making  bricks  for  lining 
furnaces,  and  for  crucibles  and  glass  pots,  as  well  as  for 
other  purposes  where  resistance  to  a  high  temperature  is 
required.  But  many  kinds  of  clay  contain  lime,  magnesia, 
or  ferric  oxide  intermixed,  and  they  greatly  increase  its 
fusibility,  and  diminish  its  plasticity,  or  fitness  for  kneading 
and  moulding  while  in  a  moist  state,  and  cause  it  to  be  more 
readily  attacked  by  acids,  while  an  excess  of  silica  renders 
it  less  fusible.  The  more  mixed  varieties  of  clay  constitute 
marl  xn.dk  loam.  Pure  clay  forms,  before  it  has  been  ignited 
and  when  kneaded  with  water,  a  tenacious  plastic  insoluble 
paste,  which,  when  slowly  dried  and  exposed  to  a  high  heat, 
shrinks  very  much,  often  splits,  and  becomes  extremely  hard, 
but  does  not  melt  in  the  furnace.  Clay  is  not  attacked  readily 
by  any  acid  except  the  hydrofluoric.  Strong  sulphuric  acid, 
when  strongly  heated  with  it,  gradually  decomposes  it. 

When  breathed  upon,  or  slightly  moistened,  clay  gives  out 
a  peculiar  odour,  and  if  applied  in  a  dry  state  to  the  tongue 
or  lips,  it  adheres  to  them  strongly,  and  absorbs  the  saliva. 

Felspar  is  a  very  abundant  and  important  double  silicate 
of  aluminum  and  potassium  (K2O,  A12O3,  6SiO2),  often 
called  adularia.  When  it  contains  sodium  it  is  white,  and  is 
termed  albite-;  and  when  it  contains  lithium,  the  mineral  is 
known  as  petalite.  Felspar  is  a  very  abundant  constituent 
of  the  older  rocks.  Mixed  with  mica  and  quartz,  it  forms 
granite  and  gneiss.  Porphyry  is  a  compact  felspar  with 
crystals  of  felspar  dispersed  through  it.  Basalt  is  a  dark- 

Q  2 


228  Pottery  Ware. 

coloured  volcanic  rock,  containing  crystals  of  augitc  diffused 
through  compact  felspar.  The  porous  pumice  of  volcanoes 
is  chiefly  felspar  altered  by  high  temperature  ;  and  obsidian 
is  melted  pumice.  Mica  is  a  more  complex  silicate  of 
alumina,  containing  a  little  fluoride. 

Earthenware  and  China. — The  basis  of  these  articles  is 
silicate  of  alumina,  but  to  diminish  the  tendency  to  crack 
during  drying,  which  it  has  if  used  alone,  the  clay  is  mixed 
with  ground  flints,  which,  however,  lessens  its  tenacity.* 
To  make  up  for  this  defect,  it  is  usual  to  add  some  fusible 
material  which,  at  the  temperature  required  for  fusing,  be- 
comes softened,  and  greatly  aids  in  binding  the  particles 
together.  The  clay  thus  mixed  and  tempered  is  moulded, 
while  moist,  upon  the  potter's  wheel,  after  which  the  dif- 
ferent articles  are  dried  in  a  warm  room,  and  are  then  fired 
at  a  comparatively  moderate  heat :  they  are  thus  obtained  in 
a  porous  state,  called  biscuit.  The  patterns  or  designs  are 
next  applied,  the  colouring  matter  consisting  usually  of  some 
metallic  oxide  ground  up  into  a  paste  with  turpentine  or 
linseed  oil  Blue  is  generally  given  by  cobalt  oxide,  green  by 
chromic  oxide,  brown  by  a  mixture  of  the  oxides  of  iron  and 
manganese,  black  by  uranium  oxide,  and  so  on.  The  ware, 
when  painted,  is  much  too  porous  for  use  ;  it  is  therefore 
glazed  by  dipping  each  article  into  water  containing  a  fusible 
mixture,  finely  ground,  in  suspension. .  The  porous  mass 
quickly  absorbs  moisture,  leaving  a  thin  uniform  layer  of 
glaze  upon  the  surface.  The  goods  are  then  enclosed  in 
fireclay  vessels,  and  exposed  to  a  furnace  heat.  The  glaze 
melts,  and  leaves  a  smooth  surface,  so  that  the  material  is 
no  longer  porous  and  absorbent. 

Stoneware  is  glazed  differently.  The  pots  are  raised  to  a 
strong  red  heat  in  the  furnace,  and  a  quantity  of  damp  salt 
is  thrown  in.  The  material  is  rapidly  volatilised.  The  salt 
is  decomposed  by  the  silica  and  ferric  oxide  of  the  clay  in 

*  In  making  crucibles  and  firebricks,  old  pots,  finely  powdered,  are 
generally  used  instead  of  ground  flints,  but  for  the  same  purpose. 


Magnesium.  229 

the  presence  of  steam.  Ferric  chloride  and  hydrochloric 
acid  pass  off  with  the  excess  of  salt  employed,  and  form  the 
dense  brownish  fumes  which  are  seen  escaping  at  intervals 
from  the  kilns  on  glazing  days,  while  sodic  silicate  fuses  on 
the  surface  of  the  ware,  and  makes  it  impervious  to  water, 
the  actions  being  as  follows  : — 

H,O      +   2NaCl  +   SiO,      =     2HC1     +   NaaO,  SiO, ;  and 
Fe,O3   +   6NaCl  +   3810,     =     Fe^    +   3(Na,O,  SiOa). 

Tests  for  Aluminum  Salts. — The  solutions  have  a  sweet, 
astringent  taste.  Potash  gives  a  white  precipitate,  soluble 
in  excess  of  the  alkali.  Ammonia,  a  white  precipitate,  in- 
soluble in  excess  of  the  alkali.  Carbonates  of  the  alkalies, 
a  white  precipitate,  insoluble  in  excess  of  the  alkaline  car- 
bonate. Ammonic  sulphide  gives  a  white  precipitate  of 
hydrated  alumina, 

Exp.  226. — Heat  a  little  alum  on  a  platinum  wire,  bent  into 
a  small  hook,  in  the  outer  flame  of  a  Bunsen  gas-burner,  After 
the  salt  has  been  touched  with  a  drop  of  a  solution  of  cobalt 
nitrate,  a  pale  blue  compound  of  alumina  and  cobalt  oxide  will 
be  formed.  It  is  used  as  a  blowpipe  reaction  for  alumina. 

2.  Glucinum  is  the  characteristic  ingredient  in  the  beryl 
and  emerald.  3.  Yttrium  and  (4)  Erbium  are  both  found 
only  in  a  few  rare  minerals.  5.  Cerium  is  met  with  rather 
more  abundantly,  accompanied  by  two  other  metals,  (6) 
Lanthanum  and  (7)  Didymium,  in  a  mineral  called  cerite, 
but  none  of  these  are  of  sufficiently  frequent  occurrence  to 
need  further  notice  here. 


GROUP  IV. — MAGNESIUM  METALS. 
i.  MAGNESIUM.    2.  ZINC.     3.  CADMIUM.    4.  INDIUM. 
(51)  i.  MAGNESIUM  :  Symbol,  Mg ;  Atom.  Wt.  24;  Sp. 
Gr.  174. 

This  metal  is  obtained  by  decomposing  its  chloride  by 
means  of  sodium.     It  is  purified  by  distilling  it  at  a  bright 


230  Compounds  of  Magnesia. 

red  heat  in  a  current  of  hydrogen.  Magnesium  is  a  malleable, 
ductile  metal,  of  the  colour  of  silver.  It  .takes  a  high  polish, 
which  it  preserves  in  a  dry  air ;  but  it  becomes  slowly  oxidized 
in  a  moist  atmosphere.  At  a  moderate  red  heat  it  melts. 

Exp.  227. — Heat  a  piece  of  magnesium  wire  in  dry  air  or  in 
the  flame  of  a  lamp  :  it  takes  fire,  and  becomes  oxidized,  pro- 
ducing white  fumes  of  magnesia,  giving  out  an  intense  white  light. 

This  light  is  occasionally  used  for  photographic  purposes, 
or  in  lighting  up  the  interior  of  buildings. 

Magnesium  is  dissolved  rapidly  by  diluted  hydrochloric 
acid,  giving  off  hydrogen  ;  and  it  is  freely  soluble  in  a  solu- 
tion of  sal  ammoniac.  When  heated  in  chlorine,  or  in  the 
vapour  of  bromine,  iodine,  or  sulphur,  it  burns  brilliantly. 

Magnesia  (MgO). — This  is  the  only  known  oxide  of  the 
metal.  It  occurs  abundantly  in  combination  as  dolomite,  or 
magnesic  calcic  carbonate  j  as  Epsom  salts,  or  sulphate ; 
as  chloride  in  sea  water;  and  as  silicate  in  a  variety  of 
forms,  both  alone,  as  in  talc  and  serpentine,  and  in  com- 
bination with  the  silicates  of  alumina  and  other  bases,  as  in 
augite,  hornblende,  and  asbestos ;  so  that  it  is  an  important 
and  frequent  constituent  of  rocks.  Magnesia  is  a  bulky, 
white,  tasteless,  and  nearly  insoluble  powder,  obtained  by 
strongly  heating  the  carbonate  or  nitrate  of  the  metal. 

Exp.  228. — Place  a  little  magnesia  on  moistened  turmeric 
paper :  it  is  sufficiently  soluble  to  render  the  parts  moistened, 
on  which  it  rests,  brown. 

Exp.  229. — Place  a  small  quantity  of  magnesic  carbonate  in  a 
crucible ;  put  on  the  cover,  and  heat  the  crucible  in  the  fire  for 
an  hour.  Take  it  out,  and  allow  it  to  cool :  caustic  magnesia 
will  be  left.  When  moistened  with  water,  it  will  not  slake ;  but 
if  hydrochloric  or  nitric  acid  be  poured  upon  the  moistened 
earth,  it  will  dissolve  slowly,  without  effervescence. 

Magnesic  Chloride  (MgCl2)  may  be  obtained  by  adding 
to  a  solution  of  one  part  of  magnesia  in  hydrochloric  acid 
three  times  its  weight  of  sal  ammoniac,  evaporating  to  dry- 
ness,  and  heating  the  mixed  salts  to  redness  in  a  covered 


Tests  for  Magnesium  Salts.  231 

crucible  :  the  magnesic  salt  fuses,  while  the  ammoniacal  salt 
goes  off  in  vapour.  This  chloride  is  deliquescent ;  but  if  its 
solution  be  evaporated  by  itself,  a  good  deal  of  hydrochloric 
escapes,  and  magnesia  is  left. 

Magnesic  Sulphate  (MgSO4,  7H2O),  familiarly  known  as 
Epsom  Salts. — This  is  the  most  important  soluble  salt  of  the 
metal.  It  crystallises  in  four-sided  solid  prisms,  which  are 
very  soluble,  and  have  a  bitter  taste. 

Tests  for  Magnesium  Salts : — 

Exp.  230. — Pour  over  25  grams  of  Epsom  salts  50  c.  c.  of 
boiling  water  :  the  salt  dissolves,  and  part  crystallises  out  as  the 
solution  cools.  To  a  portion  of  the  cold  solution  add  a  solution 
of  sodic  hydric  carbonate  :  no  precipitate  occurs.  Boil  this 
mixture,  and  a  white  precipitate  (the  white  magnesic  carbonate), 
mixed  with  magnesic  hydrate,  is  immediately  separated. 

Exp.  231. — Add  to  a  solution  of  magnesic  sulphate  some 
ammonic  chloride ;  then  add  a  solution  of  hydric  disodic  phos- 
phate. Stir  the  mixture  :  crystals  of  ammonic  magnesic  phosphate 
are  deposited  in  crystalline  grains  (MgH4N,  PO4,  6HaO),  in- 
soluble in  water,  containing  ammonia  in  solution,  but  appreciably 
soluble  in  pure  water.  This  is  a  very  delicate  test  for  mag- 
nesium salts,  but  it  is  readily  dissolved  by  acids.  Add  a  few 
drops  of  hydrochloric  acid  to  the  neutral  solution  :  the  precipi 
tate  disappears. 

Exp.  232. — Collect  a  little  of  the  crystalline  precipitate  in  a 
filter ;  dry  it  over  a  steam  bath.  Place  a  few  decigrams  of  the 
dry  salt  in  a  small  crucible,  cover  it,  and  weigh  the  whole  ;  then 
heat  it  for  ten  minutes  in  a  Bunsen  gas-flame.  Water  and  am- 
monia will  be  expelled.  Allow  the  crucible  to  cool ;  then  weigh 
it  a  second  time  :  it  will  be  found  to  have  lost  weight  con- 
siderably. The  salt  which  is  left  is  magnesic  pyrophosphate — 
2(H4NMgP04)  =  2H,N  +  HaO  +  Mg,P,O7. 

Exp.  233. — Add  to  a  solution  of  any  magnesic  salt,  such  as 
the  sulphate,  a  solution  of  potash-,  a  white  precipitate  of 
hydrated  magnesia  is  formed.  Excess  of  alkali  does  not  re- 
dissolve  it.  Limewater  produces  a  similar  precipitate.  Am- 
monic oxalate,  if  mixed  with  an  excess  of  solution  of  sal  am- 
moniac, gives  no  precipitate  with  solutions  of  magnesium  salts. 


232  Properties  of  Zinc. 

Exp.  234. — Place  a  little  of  the  magnesium  salt  on  a  platinum 
wire  moistened  with  a  solution  of  cobalt  nitrate.  A  pink  residue 
will  be  obtained  on  heating  the  wire  in  the  outer  part  of  a 
Bunsen  gas-flame. 

(52)  2.  ZINC  or  Spelter :  Symbol,  Zn  ;  Atom.  Wt.  65, 
Sp.  Gr.  7-15;  Fusing  Pt.  412. 

This  well-known  metal  occurs  chiefly  in  the  form  of  sul- 
phide, constituting  blende  (ZnS),  or  in  that  of  carbonate, 
known  to  mineralogists  as  calamine  (ZnCO3).  In  order  to 
extract  the  metal  the  sulphide  is  roasted,  or  heated  mode- 
rately in  a  current  of  air  :  the  sulphur  burns  off,  and  leaves 
the  oxide.  When  calamine  is  roasted,  water  and  carbonic 
anhydride  are  expelled,  and  zincic  oxide  is  also  left.  The 
oxide,  in  either  case,  is  next  mixed  with  powdered  coke,  and 
heated.  The  carbon  removes  the  oxygen  as  carbonic  oxide, 
while  the  zinc,  which  is  volatile  at  a  full  red  heat,  distils  over, 
and  may  be  condensed. 

Zinc  is  a  hard  bluish-white  metal,  which,  when  a  mass  of 
it  is  broken  across,  shows  a  beautiful  crystalline  fracture. 
At  ordinary  temperatures  it  is  rather  brittle ;  but  between 
100°  and  150°  it  may  be  rolled,  and  wrought  with  ease, 
though  between  200°  and  300°  it  again  becomes  brittle,  and 
may  be  powdered.  At  412°  it  melts,  and  it  boils  steadily 
at  1040°,  and  may  be  distilled  at  a  bright  red  heat. 

Exp.  235. — Heat  a  crucible  to  a  bright  red  heat,  and  throw 
into  it  a  few  fragments  of  zinc.  The  metal  will  melt,  and  give 
off  vapours  which  burn  with  great  brilliancy,  depositing  white 
clouds  of  zincic  oxide. 

Zinc  soon  tarnishes  in  a  moist  atmosphere ;  the  thin  film 
of  oxide  adheres  closely  to  the  metal,  and  protects  it  from 
further  change.  Dilute  sulphuric  and  hydrochloric  acids 
dissolve  zinc  rapidly,  and  give  off  hydrogen.  Nitric  acid 
also  attacks  it  powerfully,  but  the  acid  itself  is  at  the  same 
time  partly  decomposed. 

Zinc  is  often  used  as  a  substitute  for  lead  in  roofing ;  it  is 
lighter -and  cheaper,  but  less  durable.  It  is  also  used  as  the 


Salts  of  Zinc.  233 

active  metal  in  the  voltaic  battery,  and  becomes  dissolved 
in  proportion  as  the  electricity  is  liberated.  Sheet  iron  is 
often  coated  with  zinc,  to  render  it  less  liable  to  rust ;  it 
then  forms  what  is  called  galvanised  iron.  Brass  is  the  most 
important  of  the  alloys  of  zinc.  It  contains  about  two  parts 
of  copper  to  one  of  zinc,  but  the  proportions  of  the  two  metals 
may  be  varied  according  to  the  purpose  to  which  the  alloy 
is  to  be  applied.  German  silver  is  brass  whitened  by  the 
addition  of  nickel. 

Zinc  Oxide  (ZnO). — Zinc  forms  but  one  oxide,  which  is 
generally  obtained  in  the  form  of  a  white  flocculent  powder 
by  burning  the  metal  in  a  current  of  air.  When  heated,  this 
oxide  becomes  yellow,  but  on  cooling  it  recovers  its  white- 
ness. It  is  easily  soluble  in  the  acids.  If  a  solution  of 
potash  be  cautiously  added  to  a  solution  of  a  salt  of  zinc, 
such  as  the  sulphate,  a  white  gelatinous  hydrated  oxide  is 
precipitated,  but  it  is  redissolved  by  an  excess  of  potash  : 
ammonia  has  a  similar  effect. 

Zinc  Sulphate  (ZnSO4,  7H2O)  is  obtained  in  the  ordinary 
process  of  preparing  hydrogen  by  dissolving  zinc  in  diluted 
sulphuric  acid.  It  crystallises  in  white  soluble  prisms,  re- 
sembling those  of  magnesic  sulphate.  It  produces  vomiting 
if  swallowed  in  quantities,  such  as  one  or  two  grams. 

The  zinc  salts  are  colourless ;  they  have  an  astringent 
metallic  taste.  Sulphuretted  hydrogen  produces  no  precipi- 
tate in  their  acidulated  solutions ;  but  if  mixed  with  a 
olution  of  ammonic  sulphide,  a  white  gelatinous  zinc  sul- 
phide is  formed.  A  solution  of  sodic  carbonate  gives,  with 
zinc  salts,  a  white  precipitate  of  hydrated  basic  zinc  car- 
bonate, not  soluble  in  excess  of  the  alkaline  carbonate ;  but  if 
ammonic  carbonate  be  used  instead,  the  precipitate  is  redis- 
solved by  the  addition  of  the  ammonic  carbonate  in  excess. 
Zinc  salts  yield,  with  potassic  ferrocyanide,  a  white  pre- 
cipitate. 

Before  the  blowpipe,  in  the  reducing  flame,  on  charcoal, 
the  metal  is  reduced  and  volatilised,  burning  into  white 


234  Cadmium — Indium. 

fumes  of  the  oxide.  If  placed  on  charcoal,  and  moistened 
with  a  solution  of  cobalt  nitrate,  they  give,  when  heated  in 
the  oxidating  flame,  a  green  infusible  residue. 

3.  CADMIUM  :  Symb.  C&;Atom.  Wt.  112.— This  is  a  com- 
paratively rare  white,  soft,  easily  fusible,  volatilisable  metal, 
usually  found  as  sulphide,  accompanying  the  ores  of  zinc  in 
small  quantity.    Being  more  volatile  than  zinc,  it  comes  over 
in  the  first  portions  which  distil  over  during  the  reduction. 
It  may  be  separated  from  zinc  by  dissolving  these  portions 
of  the  metal  in  sulphuric  acid,  and  transmitting  a  stream  of 
sulphuretted  hydrogen  gas  through  the  solution  ;  a  yellow 
cadmium  sulphide  is  thus  separated.     This  precipitate  may 
be  dissolved  in  hot  hydrochloric  acid,  precipitated  from  the 
solution  by  the  addition  of  ammonic  carbonate,  and  reduc- 
ing the  carbonate  by  heating  it  in  an  earthen  retort  with 
powdered  charcoal ;  the  metal  distils  over  at  a  red  heat.     It 
takes  fire  when  heated  strongly  in  air,  and  burns,  forming  a 
brown  oxide.     The  addition  of  cadmium  to  the  more  fusible 
metals  furnishes  alloys  of  low  melting  point  without  destroy- 
ing their  toughness  and  malleability. 

Cadmium  furnisher  a  single  oxide  (CdO),  which  is  brown 
when  anhydrous,  and  white  when  hydrated.  Ammonia  dis- 
solves it  easily,  but  ammonic  carbonate  does  not  dissolve  it. 
Chloride  and  iodide  of  cadmium  are  used  by  the  photo- 
grapher. They  crystallise  easily. 

4.  Indium  is  a  white  soft  metal,  which  has  been  found  in 
small   quantity  occasionally  associated   with   zinc.     It  was 
discovered  by  its  property  of  furnishing,  when  heated  in  a 
colourless  gas-flame,  a  light  which  is  characterised  by  two 
strong  lines  in  the  indigo  portion  of  the  spectrum. 


235 


CHAPTER 

GROUP  V. — METALS  ALLIED-  TO  IRON. 

i.  COBALT.     2.  NICKEL.     3.  URANIUM.     4.  iRoJfrv^j^  CHROMIUM. 

6.  MANGANESE. 

(53)  i.  COBALT  :  Symb.  Co  ;  Atom.  Wt.  59  ;  Sp.  Gr.  8-95. 
—This  metal  is  never  used  in  the  arts  in  the  metallic  state, 
but  it  furnishes  several  compounds  which  are  much  valued 
for  their  beautiful  colour.  It  generally  occurs  in  combina- 
tion with  arsenicum,  and  is  almost  always  found  associated 
with  nickel. 

Metallic  cobalt  is  obtained  with  difficulty  in  a  pure  state 
by  a  complicated  process,  for  details  of  which  some  larger 
works  on  chemistry  should  be  consulted.  It  is  nearly  as 
infusible  as  iron,  is  of  a  reddish  grey  colour,  hard,  ductile, 
and  strongly  attracted  by  a  magnet. 

Cobalt  furnishes  several  oxides  :  two  are  well  known — the 
protoxide  (CoO),  which,  when  treated  with  acids,  yields  the 
common  salts  of  the  metal,  and  the  sesquioxide  (Co2O3). 
These  two  oxides  may  be  combined  with  each  other  in  more 
than  one  proportion. 

The  protoxide  is  soluble  in  acids,  and  forms  salts  which, 
when  anhydrous  or  in  concentrated  solutions,  are  of  a  beauti- 
ful blue  colour ;  but  they  become  pink  in  dilution.  At  a 
particular  stage  of  dilution  they  become  blue  when  heated, 
although  when  cold  the  solution  is  pink.  This  oxide  is 
largely  used  for  painting  on  porcelain,  to  which  it  imparts  a 
rich  blue  colour. 

Smalt  is  a  beautiful  blue  glass  coloured  with  this  oxide  of 
cobalt.  When  finely  powdered  it  forms  the  stone-blue  used 
by  laundresses  to  correct  the  yellow  tinge  in  linen. 

Cobalt  Nitrate  (Co2NO3,  6H2O)  is  prepared  by  dissolving 
cobalt  oxide  in  nitric  acid.     Its  solution  is  sometimes  em 
ployed  as  a  test  before  the  blowpipe.     A  fragment  of  the 
compound  suspected  to  contain  aluminum,  magnesium,  or 
zinc,  is  supported  on  charcoal,  and  touched  with  a  minute 


236  Salts  of  Cobalt— Nickel. 

quantity  of  a  solution  of  the  nitrate  :  aluminous  compounds 
give  a  blue  residue  if  heated  in  the  outer  flame,  those  of 
magnesium  a  pink,  and  those  of  zinc  a  green  residue. 

Tests  for  Salts  of  Cobalt. — All  the  compounds  of  cobalt 
are  easily  distinguished  before  the  blowpipe  by  the  intense 
blue  colour  which  they  impart,  even  in  minute  quantity,  to 
a  bead  of  borax  when  fused  with  it  on  a  loop  of  platinum 
wire.  If  the  quantity  of  cobalt  be  large,  the  colour  is  so 
intense  that  it  seems  to  be  black. 

Acid  solutions  containing  cobalt  are  not  precipitated  by 
sulphuretted  hydrogen,  but  ammonic  sulphide  yields  a  black 
sulphide  of  cobalt.  Solution  of  potash  precipitates  a  rose- 
coloured  hydrated  oxide,  insoluble  in  excess  of  the  alkali. 
Ammonia  and  its  carbonate  also  give  a  rose-coloured  pre- 
cipitate, soluble  in  excess  of  the  alkali,  forming  a  brownish 
solution,  which  absorbs  oxygen  from  the  air,  and  becomes 
red.  It  forms  one  of  a  large  series  of  ammoniacal  com- 
pounds which  contain  cobalt. 

2.  NICKEL:  Symb.  Ni;  Atom.  Wt.  59;  Sp.  Gr.  8-82.— 
This  metal  has  a  remarkable  analogy  with  cobalt.  It  occurs 
associated  with  it  in  nature,  has  the  same  atomic  weight, 
and  is,  like  cobalt,  powerfully  attracted  by  the  magnet.  Its 
most  abundant  ore  is  kupfernickel,  the  arsenide  (NiAs).  The 
mode  of  its  extraction  is  described  in  the  book  on  *  Metal- 
lurgy.' Nickel  is  a  brilliant  silver-white,  hard,  ductile  metal, 
nearly  as  infusible  as  iron.  Its  most  important  alloy  is  Ger- 
man silver,  which  is  a  kind  of  brass  whitened  by  the  addition 
of  about  20  per  cent,  of  nickel. 

There  are  two  oxides  of  nickel,  a  protoxide  (NiO)  and 
a  sesquioxide  (Ni2O3)  ;  the  first  is  the  only  one  of  importance. 
It  is  obtained  by  heating  the  nitrate  or  the  carbonate  to 
redness.  It  furnishes  an  olive-green  powder.  The  hydrated 
oxide  is  of  a  delicate  apple-green,  and  may  be  precipitated 
from  its  salts  by  the  addition  of  a  solution  of  potash,  which 
does  not  redissolve  it  when  added  in  excess.  Acids  dissolve 


Uranium — Iron.  237 

it  and  furnish  pale  green  solutions.  Ammonia  precipitates 
the  hydrated  oxide  from  these  solutions,  but,-  if  added  in 
excess,  redissolves  the  precipitate,  and  furnishes  a  blue  liquid. 
Ammonic  carbonate  precipitates  a  green  carbonate  of  nickel, 
soluble  in  excess  of  the  alkaline  carbonate. 

3.  URANIUM:  Symb.  U;  Atom.  Wt.  120. — This  metal  is 
scarcely  known  in  its  pure  state.  It  occurs  chiefly  in  the 
form  of  the  black  oxide  (2UO,  U2O3),  which  constitutes 
about  80  per  cent,  of  the  mineral  pitchblende.  The  metal 
furnishes  several  oxides.  The  black  oxide  just  mentioned 
is  used  as  an  intense  black  for  painting  on  porcelain.  The 
sesquioxide  (U2O3)  combines  with  the  alkalies  potash  and 
ammonia,  and  forms  a  yellow  compound.  It  is  also  soluble 
in  acids,  such  as  the  nitric  and  acetic,  and  forms  yellow 
salts,  the  solutions  of  which  give  a  brown  precipitate  with 
potassic  ferrocyanide,  and  a  yellow  precipitate  with  ammonia, 
not  soluble  in  excess  of  the  alkali.  This  oxide  is  used  to 
communicate  a  peculiar  opalescent  yellow  colour  to  glass, 
which  exhibits  the  optical  property  of  fluorescence  in  a  re- 
markable degree. 

(54)  4.  IRON:  Symb.  Fe ;  Atom.  Wt.  56;  Sp.  Gr.  7-84. 
—This,  the  most  important  of  the  metals,  is  also  very 
abundant.  It  is  found  now  and  then  in  the  metallic  state, 
associated  with  nickel,  cobalt,  and  some  other  elements,  in 
those  remarkable  masses  known  as  meteorites,  which  fall  in 
an  ignited  state  from  the  atmosphere  from  time  to  time — 
possibly  the  fragments  of  some  formerly  existing  planet. 
For  the  supply  of  the  vast  demand  for  iron  the  ores  chiefly 
wrought  are  magnetic  ironstone,  or  loadstone  (FeO,  Fe2O3) ; 
specular  iron  ore  (Fe2O3),  or  red  haematite,  which  is  a 
more  abundant  form  of  the  same  oxide ;  brown  haematite 
(2Fe2O3,  3H2O),  the  hydrated  sesquioxide ;  and  spathic  iron, 
or  ferrous  carbonate  (FeCO3).  This  last  is  the  material 
which,  when  mingled  with  clay,  furnishes  the  immense  de- 
posits of  clay-ironstone  which  occur  in  what  are  called  the 


238  Ores  of  Iron — Cast  Iron. 

coal  formations  of  Great  Britain.  Where  this  carbonate 
contains  bituminous  matter  instead  of  clay,  it  constitutes  the 
black-band  ironstone  of  the  coal  fields  on  the  Clyde. 

In  order  to  obtain  iron  from  the  ore,  if  in  the  form  of  clay- 
ironstone,  it  is  broken  up  into  masses  about  the  size  of  the  two 
fists,  and  then  roasted  in  heaps  to  expel  water  and  carbonic 
acid,  by  which  process  the  ore  is  left  in  a  porous  state,  highly 
favourable  to  its  reduction  in  the  blast  furnace.  These  fur- 
naces are  usually  about  fifteen  metres  high,  and  in  them  a 
mixture  of  ore,  coal,  and  limestone  is  subjected  to  intense  heat, 
fresh  supplies  being  added  at  the  top  as  the  materials  sink 
down  in  the  furnace.  Powerful  blowing  machines  supply 
air  constantly  near  the  bottom,  and  thus  a  steady  and  very 
powerful  heat  is  maintained.  The  fuel  burns,  and  is  converted 
first  into  carbonic  anhydride ;  and  this  becomes  changed  by 
the  excess  of  carbon  into  carbonic  oxide,  which,  meeting  the 
descending  charge,  reduces  its  oxide  to  metallic  iron.  The 
reduced  metal,  mixed  with  the  earthy  matter  of  the  ore,  sinks 
down  into  the  hotter  region  ;  here  the  lime,  though  infusible 
when  heated  alone,  acts  as  a  flux  upon  the  clay  of  the  ore  : 
the  two  melt  and  become  converted  into  an  imperfect  glass 
or  slag,  while  the  minutely  divided  iron  combines  with  a 
portion  of  carbon  of  the  fuel,  and  forms  the  comparatively 
fusible  material  known  as  cast  iron.  The  slag  and  melted 
iron  sink  down  to  the  bottom  of  the  furnace ;  the  iron,  being 
much  heavier,  collects  beneath  the  slag,  and  is  run  off  at 
intervals  of  twelve  or  twenty-four  hours  into  moulds  formed 
in  the  sand  of  the  floor,  and,  being  afterwards  separated 
from  each  other,  form  pigs  of  iron.  The  slag  which  collects 
on  the  surface  of  the  iron  before  it  is  run  off  flows  over 
continually  at  the  opening  left  for  the  purpose  on  a  higher 
level. 

Cast  iron,  or  pig  iron,  is  brittle,  and  cannot  be  forged, 
though,  if  run  into  moulds,  it  takes  impressions  even  of  the 
finest  lines.  It  never  contains  more  than  five  per  cent,  of 
carbon  ;  but  it  is  not  a  pure  carbide,  for  in  the  intense  heat 


Iron  and  Steel.  239 

the  carbon  of  the  fuel  reduces  not  only  the  iron  oxide,  but 
also  portions  of  silica,  alumina,  and  lime,  as  well  as  phos- 
phates and  sulphates  which  are  present.  The  cast  iron, 
therefore,  varies  much  in  its  quality,  according  as  it  contains 
more  or  less  of  carbon,  silicon,  sulphur,  phosphorus,  and  other 
elements.  When  melted  cast  iron  is  allowed  to  cool  slowly, 
part  of  the  carbon  crystallises  out,  and  remains  diffused 
through  the  mass  in  small  flakes  of  graphite.  This  variety 
of  the  metal  is  known  as  grey  cast  iron.  The  same  iron, 
if  cooled  rapidly,  is  crystalline  in  structure,  and  contains 
the  carbon  chemically  combined,  forming  what  is  known  as 
white  cast  iron. 

In  order  to  purify  the  pig  iron,  it  is  melted  in  a  current  of 
heated  air,  so  as  gradually  to  burn  off  the  carbon,  silicon, 
and  other  impurities,  which  are  more  combustible  than  the 
iron  itself,  the  carbon  escaping  as  carbonic  oxide,  the  silicon 
as  silica,  and  the  phosphorus  as  phosphates.  The  silica, 
with  the  phosphates,  unite  with  oxide  of  iron,  and  form  a 
slag.  The  metal  is  thus  rendered  less  and  less  fusible  :  it  is 
collected  by  the  workman  into  large  balls,  which  are  sub- 
jected while  white  hot  to  the  blows  of  a  powerful  hammer, 
which  squeeze  out  the  melted  slag ;  and  the  metal,  after 
being  passed  through  grooved  rollers,  becomes  converted 
into  malleable  iron,  or  wrought  iron. 

Iron,  when  combined  with  a  smaller  proportion  of  carbon 
than  is  contained  in  cast  iron,  furnishes  steel,  of  which  there 
are  several  varieties.  The  quantity  of  carbon  in  good  steel 
varies  between  07  and  17  per  cent.  That  which  possesses 
the  greatest  tenacity  has  been  found  to  contain  from  i  -3  to 
i '5  per  cent,  of  carbon  and  about  0*1  of  silicon.  Fuller 
details  of  the  mode  of  making  cast  iron,  wrought  iron,  and 
steel,  will  be  found  in  the  text  book  on  '  Metallurgy/ 

Steel  is  more  fusible  than  iron ;  it  is  brittle,  and  when 
broken  across  shows  a  fine  granular  texture;  but  its  most 
characteristic  property  is  that  of  becoming  almost  as  hard  as 
diamond  when  heated  to  redness  and  then  suddenly  cooled 


240  Properties  of  Iron. 

by  plunging  into  water  or  oil.  It  is  thus  rendered  extremely 
brittle  and  almost  perfectly  elastic.  This  extreme  hardness 
and  brittleness  may  be  removed  by  the  process  of  tempering, 
which  consists  in  reheating  the  hardened  steel  moderately, 
and  then  allowing  it  to  cool.  The  higher  the  temperature  to 
which  it  is  raised  in  the  second  heating,  the  softer  is  the 
steel. 

Exp.  236. — Allow  a  drop  of  nitric  acid  to  fall  upon  a  slip  of 
polished  steel  :  a  dark  grey  spot  is  produced,  owing  to  the  solu- 
tion of  the  metal  in  the  acid,  while  the  carbon  is  left.  If  the 
acid  be  dropped  upon  a  slip  of  iron  a  green  stain  is  formed. 

Bar  iron  generally  contains  about  0-2  per  cent,  of  carbon. 
It  is  hard,  takes  a  high  polish,  is  tough  and  fibrous,  with  a 
peculiar  bluish-grey  colour.  It  has  a  spec.  grav.  of  77. 
It  requires  the  most  intense  heat  of  a  wind  furnace  to  melt 
it.  It  passes  through  a  soft  intermediate  condition  between 
actual  fusion  and  solidity.  This  property  is  of  the  highest 
practical  importance  ;  and  it  is  owing  to  this  fact  that  the 
smith  is  enabled,  after  sprinkling  the  surface  of  two  white 
bars  with  sand,  to  weld  them  together  so  completely  that 
the  junction  is  as  tough  as  any  other  part.  The  sand  acts 
as  a  flux  to  the  layer  of  oxide  which  forms  upon  the  surface 
of  the  hot  metal.  A  slag  is  thus  formed  upon  each  bar.  By 
the  blow  of  the  hammer  the  film  of  melted  matter  is  forced 
out,  and  the  two  clean  surfaces  of  the  metal  become 
united. 

Iron  is  susceptible  of  magnetism  to  a  greater  degree  than 
any  other  known  substance.  At  a  high  temperature  it  burns 
readily,  as  is  seen  in  the  vivid  sparks  thrown  off  from  it  when 
being  forged,  and  the  brilliant  combustion  exhibited  by  a  coil 
of  watch-spring  or  of  wire,  when  heated  and  introduced  int 
oxygen  gas  (Exp.  14).  In  dry  air  polished  iron  remains 
unaltered;  but  if  exposed  to  a  moist  atmosphere,  so  that 
liquid  water  be  deposited  on  the  metal,  it  quickly  become 
rusty,  and  when  once  a  spot  of  rust  is  formed  the  action 
proceeds  rapidly.  Iron  may,  however,  be  kept  for  any 


Oxides  of  Iron.  241 

length  of  time  unchanged  in  water  quite  free  from  air,  as 
well  as  in  lirnewater,  or  in  water  containing  a  little  caustic 
alkali.  If  steam  be  passed  over  red-hot  iron,  minute  crystals 
of  the  magnetic  oxide  are  formed,  and  hydrogen  is  given  off 
(Exp.  44,  Fig.  13). 

Chlorine,  bromine,  and  iodine  combine  quickly  with  iron, 
and  dissolve  it  easily  at  common  temperatures,  as  may  be 
easily  seen  by  placing  a  few  drops  of  bromine  under  water 
in  a  test-tube  and  allowing  a  small  quantity  of  iron  filings  to 
fall  into  the  bromine.  The  iron  will  disappear,  with  a  strong 
evolution  of  heat.  Diluted  sulphuric  and  hydrochloric  acid 
dissolve  the  metal  with  escape  of  hydrogen  (Exp.  45  and 
p.  60).  The  metal  is  rapidly  attacked  by  nitric  acid,  with 
abundant  escape  of  nitric  oxide.  Iron  may,  however,  be 
kept  unaltered  in  nitric  acid  of  sp.  gr.  i  -45,  or  upwards  ; 
but  if  the  acid  be  diluted  below  1*35,  it  dissolves  the  metal 
with  violence. 

Iron  yields  four  definite  oxides :  i.  The  protoxide  (FeO), 
the  base  of  the  green  or  ferrous  salts  ;  2.  The  sesquioxide, 
the  base  of  the  red  or  ferric  salts  ;  3.  The  black  or  magnetic 
oxide  (FeO,  Fe2O3),  a  compound  of  the  two  preceding 
oxides,  which,  when  treated  with  acids,  yields  a  mixture  of 
ferrous  and  ferric  salts,  but  no  distinct  saline  compounds 
referable  to  it  in  constitution ;  and  4.  Ferric  Acid,  an 
unstable  metallic  acid,  the  anhydride  of  which  is  unknown, 
but  which  forms  salts,  of  which  potassic  ferrate  (K2FeO4)  is 
the  representative. 

Ferrous  Oxide  (FeO)  is  scarcely  known  in  a  pure  state,  it 
absorbs  oxygen  so  rapidly.  It  forms  a  white  hydrate ;  and  if 
obtained  by  adding  an  alkali,  such  as  ammonia,  to  a  solution 
of  ferrous  sulphate,  the  white  precipitate  becomes  green, 
passing  into  bluish  green,  black,  and  finally  ochre-coloured, 
by  the  formation  of  sesquioxide.  Ferrous  salts,  such  as  the 
chloride  or  sulphate,  are  obtained  by  dissolving  the  metal  or 
its  sulphide  in  hydrochloric  or  sulphuric  acid,  and  allowing 
the  solution  to  crystallise  out  of  contact  with  air.  These 

R 


242  Sulphides  of  Iron. 

salts  have  a  delicate  bluish-green  colour,  and  an  astringent, 
inky  taste.  If  exposed  to  the  air  while  moist,  they  become 
grass  green,  and  slowly  absorb  oxygen. 

Ferric  Oxide  (Fe2O3)  is  an  abundant  ore  of  iron.  When 
anhydrous  and  crystallised,  it  forms  specular  iron  ore.  When 
in  masses  it  furnishes  haematite.  Brown  haematite,  a  hydrate 
(2F2O3,  3H2O),is  another  abundant  and  valuable  ore.  In 
this  form  it  is  readily  dissolved  by  acids.  Jewellers'  rouge  is 
a  finely-powdered  red  oxide,  obtained  by  igniting  the  sulphate, 
as  in  the  process  for  preparing  the  Nordhausen  oil  of  vitriol. 

When  a  ferric  salt  in  solution,  such  as  the  chloride,  is 
mixed  with  potash  or  ammonia,  a  milky  reddish-brown 
hydrated  ferric  oxide  is  precipitated. 

Iron  combines  with  sulphur  in  several  proportions.  The 
Protosulphide  (FeS)  may  be  obtained  as  follows  : — 

Exp.  237. — Heat  a  bar  of  iron  white  hot  in  the  fire,  and  bring 
it  in  contact  with  a  roll  of  sulphur  over  a  pail  of  cold  water. 
The  sulphur  and  iron  immediately  unite,  and  form  drops  of  a 
reddish-brown  colour,  which  run  down  into  the  water. 

This  sulphide  is  used  in  the  laboratory  for  preparing 
sulphuretted  hydrogen,  which  is  disengaged  without  heat, 
by  pouring  upon  it  sulphuric  acid  diluted  with  5  or  6  times 
its  bulk  of  water. 

The  Disulphide  (FeS2)  is  an  abundant  natural  product.  It 
forms  the  yellow  brassy-looking  mineral  known  as  iron 
pyrites,  often  found  crystallised  in  cubes. 

Exp.  238. — Place  a  few  fragments  of  pyrites  in  a  small  sealed 
tube,  and  heat  it  to  dull  redness  in  a  lamp-flame  ;  sulphur  will 
gradually  be  sublimed. 

When  heated  in  the  air  the  sulphur  burns  off,  and  furnishes 
sulphurous  anhydride,  which  is  largely  prepared  from  it  for 
conversion  into  sulphuric  acid.  An  impure  oxide  of  iron  is 
then  left.  Iron  pyrites  is  not  easily  dissolved,  except  by 
nitric  acid,  or,  still  better,  by  a  mixture  of  nitric  with  hydro- 
chloric acid.  Mispickel  (FeAsS)  is  the  name  given  to  an 
arsenic  sulphide  of  iron,  which  furnishes  a  good  deal  of  the 


Tests  for  Iron.  243 

arsenic  of  commerce.  When  heated  in  a  current  of  air,  it  is 
converted  into  ferric  oxide,  while  sulphurous  and  arsenious 
anhydrides  are  produced. 

A  solution  of  a  ferrous  salt,  such  as  the  sulphate,  when 
mixed    with   ammonic   sulphide,  yields   a   black   hydrated 
ferrous  sulphide,  and  in  a  similar  way  a  solution  of  a  ferric 
salt,  such  as  the  chloride,  yields  a  hydrated  sesquisulphide — 
FeSO4   +    (H4N)2S          =     (H4N)2SO4   +   FeS;    and 
Fe2Cl6    +   3[(H4N)2S]     =     6H4NC1        +    Fe2S3. 

Both  these  sulphides,  when  exposed  to  the  air,  become 
converted  into  hydrated  oxide,  while  the  sulphur  is  separated 
without  undergoing  oxidation — 

4(FeS,  H20)   +   302     =     2(Fe2O3,  2H2O)  +   28* 

Ferrous  Chloride  (FeCl2,  4H2O)  may  be  obtained  by  dis- 
solving the  metal  in  hydrochloric  acid,  and  evaporating  the 
solution  till  it  crystallises.  Ferric  Chloride,  formerly  known 
as  sesquichloride  (Fe2Cl6),  may  be  obtained  sublimed  in 
anhydrous  brown  scales  by  heating  iron  wire  to  redness  in 
a  current  of  dry  chlorine  gas ;  it  is  very  deliquescent.  A 
solution  of  ferric  chloride  may  also  be  obtained  by  passing  a 
current  of  chlorine  gas  through  a  solution  of  ferrous  chloride 
as  long  as  the  gas  is  absorbed,  or  it  may  be  procured  by  dis- 
solving hydrated  ferric  oxide  in  hydrochloric  acid. 

Ferrous  Carbonate  (FeCO3)  is  found  native  in  immense 
quantities.  When  crystallised,  it  is  known  as  spathic  iron  ore  ; 
when  mixed  with  clay,  it  forms  the  clay-ironstone  ;  and 
when  with  bituminous  matter,  furnishes  the  blackband  iron- 
stone. Ferrous  carbonate  is  also  the  salt  which  is  found  in 
chalybeate  springs,  in  which  it  is  held  in  solution  by  free 
carbonic  acid.  Mere  exposure  to  air  then  causes  its  sepa- 
ration :  the  acid  escapes,  oxygen  is  absorbed,  and  hydrated 
ferric  oxide,  mixed  with  a  small  quantity  of  organic  matter, 
subsides,  forming  the  ochry  deposits  so  common  around 
ferruginous  springs. 

Tests  for  Iron. — The  salts  of  this  metal  have  an  inky  and 
astringent  taste.  The  ferrous  salts  are  known  by  the  deep 


244  Compounds  of  Chromium. 

blue  precipitate  which  they  give  with  the  red  prussiate 
(potassic  ferricyanide)  in  solution.  If  one  of  the  ferrous 
salts  be  boiled  with  nitric  acid,  it  is  converted  into  a  solution 
of  ferric  salt,  while  one  of  the  lower  oxides  of  nitrogen 
escapes.  Ferric  salts  in  solution  are  known  by  the  rusty-brown 
precipitate  of  hydrated  ferric  oxide  which  they  give  with 
ammonia,  by  the  blood-red  solution  produced  by  potassic 
sulphocyanide  when  added  to  an  acid  or  neutral  solution,  by 
the  bright  Prussian  blue  precipitate  occasioned  by  a  solution 
of  yellow  potassic  ferrocyanide,  and  by  the  bluish-black  inky 
precipitate  produced  by  tincture  of  galls  in  neutral  solutions. 
This  last  is  the  colouring  matter  in  ordinary  writing-ink. 
Potassic  ferricyanide  gives  no  precipitate  in  ferric  solutions, 
and  thus  may  be  used  to  distinguish  them  from  those  of 
ferrous  salts. 

Exp.  239. — Add  to  a  solution  of  a  ferric  salt,  mixed  with  a  little 
solution  of  a  salt  of  cobalt,  a  weak  solution  of  ammonia,  drop 
by  drop,  stirring  the  liquid  between  each  addition,  until  the  pre- 
cipitate just  begins  no  longer  to  be  dissolved.  The  solution  will 
become  of  a  deeper  red  or  yellow  tinge.  Dilute  the  liquid  freely 
with  water,  and  then  boil  it ;  an  insoluble  basic  salt  of  iron  will 
be  formed,  and  every  trace  of  iron  may  thus  be  precipitated, 
whilst  the  cobalt  will  remain  dissolved,  and  may  be  found  by 
adding  a  little  more  of  ammonia. 

(55)  5-  CHROMIUM  (Symb.  Cr;  At.  Wt.  52-5)  is  never 
used  as  a  metal,  or  even  as  an  alloy,  but  is  highly  prized  for 
the  numerous  brilliant-coloured  compounds  which  it  forms. 
The  name  chromium  is  derived  from  xp&pa,  colour.  It  is  a 
rather  rare  element,  and  is  most  usually  found  in  the  chrome 
ironstone  (FeO,  Cr2O3). 

The  metal  is  very  hard  and  infusible.  It  is  sometimes 
obtained  by  heating  chromic  chloride  with  sodium.  Chromium 
forms  four  well-known  oxides :  chromous  oxide  (CrO),  which  is 
unimportant ;  chromic  oxide  (Cr2O3),  the  basis  of  the  common 
green  or  violet  salts  of  the  metal  :  it  is  prized  as  a  green 
pigment  for  colouring  porcelain  (these  two  oxides  corre- 


Salts  of  Chromium.  245 

spend  to  ferrous  and  ferric  oxide  in  composition);  a  brown 
oxide  (CrO,  Cr2O3),  corresponding  with  the  magnetic  oxide 
of  iron,  but  which  is  unimportant ;  and  a  stable  metallic 
anhydride  (CrO3),  which,  when  dissolved  in  water,  furnishes 
an  important  acid,  from  which  the  class  of  chromates  is 
obtained. 

The  chromates  are  prepared  on  a  large  scale  by  heating 
chrome  ironstone  to  redness,  quenching  in  cold  water  to 
render  it  friable,  then  reducing  it  to  an  extremely  fine 
powder,  and  heating  to  bright  redness  in  a  current  of  air, 
with  a  mixture  of  chalk  and  potassic  carbonate.  The  mixture 
absorbs  oxygen,  and  becomes  yellow.  When  cold,  it  is 
treated  with  water,  which  dissolves  out  the  chromates. 
Potassic  carbonate  is  added  as  long  as  it  occasions  any  pre- 
cipitate of  chalk  from  the  solution  of  calcic  chromate.  The 
yellow  solution  is  drawn  off,  mixed  with  nitric  acid,  and  on 
evaporation  potassic  dichromate  crystallises  out  in  large  red 
anhydrous  prisms  (K2CrO4,  CrO3),  whilst  nitric  acid  remains 
in  solution. 

This  dichromate  is  the  common  commercial  salt.  It  is  a 
salt  of  exceptional  composition,  being  a  compound  of  the 
chromic  anhydride  with  the  normal  potassium  salt.  If 
formed  in  the  regular  way  it  would  be  composed  as  follows  : 

KHCrO4,  or  K2CrO4,  H2CrO4  ; 

but  such  a  salt  is  not  known.  The  dichromate  is  soluble 
in  about  ten  parts  of  cold  water.  If  4  measures  of  the  cold 
saturated  solution  of  this  salt  be  mixed  with  5  of  oil  of 
vitriol,  and  the  liquid  be  allowed  to  cool,  chromic  anhydride 
crystallises  in  crimson  needles,  which  may  be  drained  and 
dried  upon  a  brick. 

Besides  the  dichromate,  there  is  a  normal  chromate  of 
potassium  (K2CrO4),  which  is  yellow,  and  does  not  crystal- 
lise easily;  and  there  are  also  potassic  salts  known  which 
contain  two  and  three  atoms  of  chromic  anhydride  combined 
with  one  atom  of  the  normal  salt. 

Baric  chromate  is  a  canary-yellow  insoluble  powder. 


246  Oxides  of  Manganese. 

Chrome  Yellow  is  the  normal  lead  chromate  (PbCrO4).  It 
falls  as  a  bright  yellow  insoluble  powder  when  a  solution 
of  lead  acetate  or  lead  .nitrate  is  mixed  with  one  of  potassic 
chromate  or  dichromate.  Argentic  chromate  (Ag2CrO4)  is 
of  a  dark  red  colour,  and  is  insoluble.  Mercurous  chromate 
(3Hg2CrO4,  Hg2O),  obtained  by  adding  mercurous  nitrate 
to  a  solution  of  a  chromate,  is  orange  coloured  and  nearly  in- 
soluble. The  chromates  of  cadmium  and  bismuth  are  yellow. 

If  a  soluble  chromate,  such  as  potassic  chromate,  be 
mixed  with  hydrochloric  acid,  chromic  acid  and  a  chloride 
of  the  metal  are  formed  in  the  solution ;  and  if  a  little  alcohol 
or  sugar  be  added,  and  the  liquid  be  boiled,  it  becomes 
green,  owing  to  the  reduction  of  the  chromic  acid  to 
chromic  oxide,  which  becomes  dissolved  in  the  excess  of 
hydrochloric  acid.  If  to  this  green  solution  ammonia  be 
added  in  excess,  a  pale  green  hydrated  chromic  oxide  is 
precipitated.  This  may  serve  as  a  distinctive  test  for  the 
chromates. 

6.  MANGANESE  :  Symbol,  Mn ;  Atomic  Weight,  55. — 
This  is  an  element  which  is  widely  diffused,  and  enters 
into  the  formation  of  many  minerals  in  small  quantity,  but 
its  only  important  and  valuable  ore  is  the  black  oxide,  found 
either  in  masses  or  in  radiated  groups  of  crystals. 

The  metal  is  not  used  alone,  but  it  is  often  present  in 
small  quantity  in  cast  iron.  It  is  difficult  to  obtain  manganese 
in  a  state  of  purity,  as  it  possesses  a  powerful  attraction 
for  carbon,  so  that,  if  reduced,  as  it  may  be  without  much 
difficulty,  by  making  the  carbonate  into  a  paste  with  oil, 
and  heating  it  in  a  covered  crucible  lined  with  charcoal,  and 
keeping  it  for  an  hour  at  the  highest  heat  of  a  forge,  the 
button  of  metal  is  always  combined  with  carbon.  It  also, 
like  iron,  combines  with  silicon.  Manganese  is  a  hard, 
brittle,  greyish-white  metal,  and  is  feebly  magnetic.  It  is 
remarkable  for  the  number  of  oxides  which  it  forms.  Man- 
ganous  oxide  (MnO)  is  the  basis  of  the  common  salts  of  the 


Compounds  of  Manganese.  247 

metal ;  the  sesquioxide  (Mn2O3)  is  unimportant,  and  does 
not  furnish  stable  salts.  The  red  oxide  (Mn3O4)  may  be 
regarded  as  the  compound  of  the  two  preceding  ones  ;  it 
corresponds  to  the  magnetic  oxide  of  iron,  and  furnishes  no 
corresponding  salts.  The  black  oxide  or  dioxide  (MnO2) 
is  the  most  important  native  compound  of  the  metal ;  when 
treated  with  acids,  it  gives  off  half  its  oxygen,  and  furnishes 
manganous  salts — 

2MnO2    +   2H2SO4     —     2MnSO4   +   2H2O   +   O2. 

With  hydrochloric  acid  it  yields  chlorine  and  manganous 
chloride — 

MnO2  +  4HC1     ±=     MnCl2   +   2H2O   +   C12 ; 

and  if  heated  alone,  it  yields  oxygen  and  the  red  oxide, 
givirkg  off  one-third  of  its  oxygen — 

3MnO2     =     Mn3O4   +   O2. 

When  found  native,  it  is  called  grey  manganese  ore,  or pyro- 
lusite.  Another  variety,  in  warty  masses,  is  psilomelane,  and 
a  hydrated  form  is  called  wad.  it  is  often  found  mixed 
with  earthy  carbonates,  and  other  impurities.  Besides  the 
above-mentioned  oxides,  manganese  forms  two  others,  which 
are  not  known  in  a  separate  state  (MnO3  and  Mn2O7),  which, 
when  dissolved  in  water,  furnish  manganic  and  permanganic 
acids.  The  manganates  are  of  a  green  colour.  Sodic  Man- 
ganate  (Na2MnO4)  is  prepared  on  a  large  scale  by  heating  a 
mixture  of  caustic  soda  and  finely-powdered  manganese  to 
dull  redness  for  several  hours  in  shallow  vessels.  Its  solu- 
tion forms  Condy's  green  disinfecting  liquid.  This  green 
substance  furnishes  an  excellent  method  of  distinguishing 
,  before  the  blow-pipe,  for  if  the  substance  be  heated  on  pla- 
tinum foil,  with  a  little  sodic  carbonate,  it  gives  a  green 
colour  to  the  melted  mass  if  a  trace  of  manganese  be 
present. 

Solutions  of  the  manganates  part  very  readily  with  oxygen : 
they  must  not  even  be  filtered  through  paper.  A  small 
quantity  of  a  free  acid  changes  their  solution  from  green  to 


248  Tests  for  Manganese. 

red,  owing  to  the  formation  of  a  permanganate  and  of  a 
manganous  salt — 

5K2MnO4   +   4HaSO4     = 
2KaMn2O8   +   MnSO4   +   3K3SO4   +   4HaO. 

Potassic  Permanganate  (K2Mn2O8)  may  be  obtained  on  a 
small  scale  by  mixing  40  grams  of  finely-powdered  man- 
ganese dioxide  with  35  grams  of  potassic  chlorate,  and 
adding  a  solution  of  50  grams  of  caustic  potash  to  the  mix- 
ture, evaporating  to  dryness,  and  heating  the  powdered 
residue  to  dull  redness  in  a  clay  crucible.  When  cold,  the 
mass  is  treated  with  water,  and  decanted  from  the  insoluble 
residue  ;  a  splendid  purple  liquid  is  obtained,  which  on 
evaporation  yields  needles  of  the  permanganate.  A  solu- 
tion of  this  salt  is  very  readily  deoxidised  and  deprived  of 
colour.  It  furnishes  a  valuable  test  liquid  in  many  cases  of 
volumetric  analysis. 

Exp.  240. — Dissolve  two  or  three  decigrams  of  iron  wire  in 
diluted  sulphuric  acid  ;  then  add  water  till  the  liquid  measures 
about  half  a  litre.  Add  gradually  a  solution  of  the  permanganate, 
and  stir  the  mixture :  the  colour  will  disappear  until  the  whole  of 
the  iron  has  passed  from  the  state  of  ferrous  into  that  of  ferric 
salt.  When  this  point  is  reached,  the  pink  colour  of  the  per- 
manganate will  remain  unchanged. 

The  change  may  be  thus  represented — 

ioFeSO4   +   K2Mn2O8   +   8H2SO4     « 
5Fe2sS04   +    K2S04   +   2MnSO4   +   8H2O. 

Tests  for  Manganese. — Manganous  chloride  is  formed  in 
large  quantities  in  the  ordinary  mode  of  preparing  chlorine. 
The  manganous  salts  are  of  a  delicate  pink  colour,  and  give 
nearly  colourless  solutions.  They  give  with  ammonia  a 
white  hydrated  manganous  oxide,  soluble  in  excess  of  the 
alkali;  but  the  solution  quickly  absorbs  oxygen,  and  deposits 
a  brown  hydrated  peroxide.  Ammonic  sulphide  precipi- 
tates a  flesh-coloured  hydrated  manganous  sulphide.  Solu- 
tion of  potassic  carbonate  precipitates  a  white  manganous 
carbonate.  Before  the  blowpipe  they  give,  with  sodic  car- 


Tin.  249 

bonate  on  platinum  foil,  the  characteristic  green-coloured 
manganate ;  and  they  give  in  the  oxidising  flame,  with  a 
bead  of  borax,  a  violet  colour,  which  disappears  in  the  re- 
ducing flame. 


CHAPTER  XIV. 

GROUP  VI. — TIN  AND  ALLIED  METALS. 
i.  TIN.     2.  TITANIUM.     3.  ZIRCONIUM.     4.  THORINUM, 

(56)  TIN:  Symb.  Sn;  Atom.  Wt.  118;  Sp.  Gr.  7-29; 
Fusing  PL  228°. 

This  familiar  metal  was  known  in  the  early  ages  of  the 
world.  It  is  not  found  in  many  places,  Cornwall  and 
Malacca  supplying  the  greatest  portion.  The  only  ore  of  tin 
of  importance  is  its  dioxide,  or  tinstone,  which  is  often  found 
crystallised.  After  the  ore  has  been  crushed,  and  roasted  to 
get  rid  of  arsenicum  and  sulphur,  and  washed  to  remove 
the  oxides  of  iron  and  copper  which  are  formed  from  the 
pyrites  by  which  it  is  accompanied,  the  metal  is  reduced 
by  heating  the  residue  with  powdered  anthracite  or  char- 
coal. 

Tin  is  a  white  metal,  with  a  tinge  of  yellow,  and  a  high 
lustre,  which  it  preserves  unchanged  in  the  atmosphere.  It 
is  rather  soft,  and  very  malleable,  so  that  it  is  easily  reduced 
into  sheets  of  tinfoil,  but  it  is  not  sufficiently  tough  to  be 
drawn  readily  into  wire.  It  melts  easily  (about  228°  C.),  but 
is  not  volatilised  in  the  furnace.  It  has  a  considerable 
tendency  to  crystallise. 

Exp.  241. — Warm  a  sheet  of  tinplate  over  a  lamp,  and  then 
pour  over  its  surface  a  mixture  of  nitric  and  hydrochloric  acids 
diluted  with  8  or  10  parts  of  water.  In  a  few  minutes  crystalline 
flakes  will  appear.  They  may  be  rendered  permanent  by  wash- 
ing off  the  acid,  drying  the  plate,  and  varnishing  it. 

If  heated  to  bright  redness  in  the  air,  tin  burns  with  a  white 
light,  and  furnishes  the  dioxide. 


250  Oxides  of  Tin. 

Hydrochloric  acid,  if  heated  with  tin,  dissolves  it  slowly, 
with  escape  of  hydrogen,  forming  stannous  chloride  (SnCl2), 
one  of  its  most  important  salts.  Nitric  acid  of  sp.  gr.  1*3 
oxidises  it  violently,  and  forms  a  white  hydrated  oxide,  known 
as  metastannic  acid,  but  does  not  form  a  nitrate.  Tin  also 
combines  easily  with  sulphur,  phosphorus,  chlorine,  and 
bromine,  when  heated  with  them. 

Tin  forms  several  important  alloys.  Tinplate  consists  of 
sheet  iron  which  has  been  cleansed  from  oxide,  and  coated 
with  tin  by  plunging  it  into  a  bath  of  the  melted  metal 
Pewter  is  an  alloy  of  4  parts  of  tin  and  i  of  lead.  Plumbers1 
solder  is  a  fusible  alloy  of  equal  parts  of  tin  and  lead. 
Britannia  metal  is  composed  of  equal  parts  of  brass,  tin, 
antimony,  and  bismuth  ;  it  is  much  used  for  making  common 
spoons  and  teapots. 

Copper  and  tin  form  several  valuable  alloys.  Bronze  is 
a  combination  of  copper,  tin,  and  zinc,  with  5  or  6  per  cent, 
of  tin  and  3  or  4  of  zinc.  Gun  metal  contains  9  or  10  per 
cent,  of  tin,  bell  metal  about  22  per  cent,  and  speculum  metal 
about  33  per  cent.  Tinfoil,  when  amalgamated  with  mer- 
cury, forms  the  silvering  applied  to  the  backs  of  mirrors. 

Tin  forms  two  oxides,  stannous  oxide  (SnO)  and  stannic 
oxide  (SnO2).  The  Stannous  Oxide  may  be  obtained  as  a 
white  hydrate  by  adding  a  solution  of  sodic  carbonate  to  one 
of  stannous  chloride  :  carbonic  anhydride  escapes,  and  the 
hydrated  tin  oxide  is  precipitated.  It  is  soluble  in  an  excess 
of  caustic  potash,  but  not  in  excess  of  ammonia.  This 
oxide,  when  moist,  absorbs  oxygen  from  the  air.  It  is  soluble 
in  acids,  and  furnishes  the  stannous  salts,  of  which,  how- 
ever, stannous  chloride  is  the  only  one  of  considerable  im- 
portance. 

Stannic  oxide,  the  dioxide  (SnO2),  constitutes  the  ore  of 
tin.  It  is  in  this  form  very  hard,  and  is  insoluble  in  acids ; 
but  when  powdered  and  fused  with  potash  or  soda,  it  com- 
bines with  the  alkali,  and  becomes  soluble  in  water.  When 
combined  with  water,  this  oxide  furnishes  a  feeble  metallic 


Compounds  of  Tin.  251 

acid,  which  is  itself  readily  soluble  in  diluted  acids,  though 
it  furnishes  salts  called  stannates. 

Sodic  Stannate  (Na2SnO3,  3H2O)  may  be  prepared  by 
fusion,  as  above  described  ;  it  is  used,  under  the  name  of 
tin-prepare  liquor,  by  the  calico  printer  as  a  mordant  for 
fixing  certain  colours. 

Another  hydrate  of  this  oxide,  possessed  of  entirely  dif- 
ferent properties,  is  obtained  by  treating  metallic  tin  with  nitric 
acid.  It  is  called  Metastannic  Acid  (H2Sn5On,  4H2O),  and 
is  quite  insoluble  in  other  acids.  It  also  forms  unstable 
salts,  such  as  potassic  metastannate  (K2Sn5Ou,  4H2O). 
When  metastannic  acid  is  heated  to  redness,  it  loses  all  its 
water,  and  furnishes  a  pale  buff-coloured  substance,  some- 
times called  putty  powder. 

Tin  forms  two  well-marked  sulphides.  Stannous  Sulphide 
(SnS)  is  thrown  down  as  a  chocolate-brown  hydrate  when  a 
stream  of  sulphuretted  hydrogen  is  passed  through  a  solution 
of  stannous  chloride  or  other  stannous  salt.  It  is  dissolved 
by  a  solution  of  ammonic  disulphide. 

Stannic  Sulphide  (SnS2)  may  be  obtained  as  a  hydrate,  of 
a  dingy  yellow  colour,  by  transmitting  sulphuretted  hydrogen 
through  a  solution  of  a  stannic  salt,  such  as  stannic  chloride ; 
and  it  is  readily  dissolved  by  ammonic  sulphide,  with  which 
it  forms  a  soluble  double  sulphide.  A  similar  double  salt 
may  be  obtained  in  crystals  (2Na2S,  SnS2,  i2H2O),  if  sodic 
sulphide  be  used  as  the  solvent. 

Stannic  sulphide  may  be  obtained  in  beautiful  yellow 
flakes,  forming  mosaic  gold,  by  heating  an  amalgam  of  tin 
with  sulphur  and  sal  ammoniac ;  but  the  operation  requires 
care. 

Stannous  Chloride  (SnCl2,  2H2O),  the  tin  salts  of  the  dyer, 
may  be  obtained  crystallised  in  needles  by  dissolving  tin  in 
strong  hydrochloric  acid,  and  evaporating  the  liquid.  It  has 
a  strong  attraction  both  for  chlorine  and  for  oxygen.  It 
therefore  acts  as  a  powerful  reducing  agent. 

Exp.  242. — Add  to  a  solution  of  corrosive  sublimate  a  drop 


252  Tests  for  Tin. 

or  two  of  a  solution  of  stannous  chloride :  a  white  precipitate  of 
calomel  is  formed — 

2HgCla   +   SnCla   =   2HgCl   +   SnCl4. 

Now  add  the  tin  salt  in  excess  :  the  precipitate  becomes  dark 
grey.  It  consists  of  metallic  mercury,  which  may  be  collected 
into  globules — 

2HgCl   +    SnCla   =   2Hg   +   SnCl4. 
The  calomel  loses  the  whole  of  its  chlorine. 

Stannous  chloride  is  used  by  the  dyer  for  deoxidising 
indigo  and  the  peroxides  of  iron  and  manganese. 

Stannic  Chloride  (SnCl4)  is  a  colourless  liquid,  which  emits 
dense  fumes  in  the  air,  boiling  at  115°  C,  and  combining  with 
water  greedily,  to  form  a  crystalline  hydrate,  which  is  soluble 
in  a  further  quantity,  but  is  decomposed  by  copious  dilution, 
stannic  acid  being  precipitated,  while  hydrochloric  acid  is  set 
free.  The  precipitate  is  readily  redissolved  by  an  excess  oi 
acid.  Stannic  acid  is  easily  obtained  from  this  chloride  by 
the  cautious  addition  of  sodic  carbonate  to  the  solution. 
This  chloride  is  prepared  without  difficulty  by  distilling 
i  part  of  tin  filings  with  4  parts  of  corrosive  sublimate, 
2HgCl2  +  Sn  yielding  SnCl4  -f  2Hg.  Exposure  to  the  fumes 
must  be  carefully  avoided. 

Tests  for  Tin. — In  addition  to  reactions  mentioned  when 
speaking  of  stannous  oxide  and  stannous  chloride,  the  stan- 
nous salts  are  characterised  by  giving  in  a  dilute  solution,  if 
mixed  with  a  solution  of  auric  chloride,  a  beautiful  purple 
precipitate,  '  the  purple  of  Cassius ' ;  but  if  the  tin  salt  be 
in  excess,  a  brown  precipitate  of  reduced  gold  is  formed. 
Before  the  blowpipe  on  charcoal,  tin  salts  yield  a  malleable 
white  bead  of  the  metal. 

Tin  belongs  to  the  group  of  tetrad  elements,  and  presents 
a  certain  analogy  with  silicon  in  its  mode  of  combination. 
It  is  still  more  closely  allied  to  the  rare  bodies  titanium,  zir- 
conium, and  thorinum,  which,  however,  are  not  of  sufficient 
practical  importance  to  need  notice  here. 

Molybdenum  is  found  as  a  sulphide  resembling  blacklead 


Arsenicum.  253 

in  appearance  ;  and  tungsten  in  a  heavy,  black,  hard  mineral, 
called  wolfram.  It  is  unnecessary  to  describe  further  the 
compounds  of  molybdenum  and  tungsten,  or  those  of  colum- 
bium,  tantalum,  and  vanadium  :  for  particulars  respecting 
them  the  reader  is  referred  to  systematic  treatises  on 
Chemistry. 


CHAPTER   XV. 

I.    ARSENICUM.       2.    ANTIMONY.       3.    BISMUTH. 

(57)  i.  ARSENICUM  :  Symb.  As;  Atom.  Wt.  75;  Sp.  gr. 
of  solid,  5-95 ;  of  vapour,  io'6  ;  Atow.  Vol.  \,  or^\ ;  Mol.  Vol. 
£3,As4;^/.  JT/.  150. 

This  highly  poisonous  substance  exhibits  characters  inter- 
mediate between  those  of  the  non-metals  and  the  metals.  It 
conducts  electricity  in  a  moderate  degree,  and  possesses 
high  metallic  brilliancy ;  but  it  much  resembles  phosphorus 
in  general  properties,  including  its  anomalous  vapour  density. 
It  is  usually  found  in  the  form  of  an  alloy  with  some  other 
metal,  especially  with  iron,  cobalt,  nickel,  or  copper.  Now 
and  then  it  is  found  native,  and  occasionally  in  the  form  of 
a  metallic  arseniate. 

In  the  preparation  of  the  metal  native  arsenide  of  iron  or 
of  cobalt  is  roasted,  or  heated  in  a  current  of  air.  The  - 
arsenicum  becomes  oxidized,  and  forms  arsenious  anhydride 
(As2O3),  or  white  arsenic,  which  is  volatilised  below  a  red 
heat,  and  becomes  condensed  again  as  it  cools  in  the  flues, 
or  in  chambers  constructed  to  receive  it. 

In  order  to  obtain  the  metal,  this  white  oxide  is  powdered, 
mixed  with  charcoal,  and  heated  in  a  crucible,  upon  the  top 
of  which  a  second  inverted  crucible  is  luted  ;  and  this  is 
screened  from  the  fire  by  means  of  a  perforated  iron  plate. 
Carbonic  oxide  is  formed,  and  escapes,  while  the  metal, 
which  is  also  volatile  below  redness,  sublimes,  and  is  con- 
densed in  the  cool  inverted  crucible.  The  metal,  however, 


254  Arsenicum. 

is  not  often  wanted.  It  is  very  poisonous,  both  alone  and 
when  in  combination,  and  requires  great  care  in  experiment- 
ing with  it. 

Exp.  243. — Take  a  fragment  of  white  arsenic,  the  size  of  a 
pin's  head ;  crush  it  to  a  fine  powder,  and  mix  it  with  3  or  4  times 
its  bulk  of  powdered  charcoal.  Introduce  the  mixture  into  a  glass 
quill  tube,  sealed  at  one  end  and  8  or  10  cm.  long.  Warm  the 
mixture  gently,  so  as  to  drive  off  the  moisture  which  the  char- 
coal usually  contains.  This,  when  condensed,  may  be  removed 
from  the  tube  by  introducing  a  small  roll  of  filtering-paper. 
Then  heat  the  end  of  the  tube  containing  the  mixture  to  red- 
ness. A  dark  steel-grey  metallic  mirror-like  sublimate  of  reduced 
arsenicum  will  be  condensed  on  the  cool  sides  of  the  tube,  and 
a  distinct  garlic-like  odour  will  generally  be  perceived. 

Arsenicum  is  very  brittle;  it  has  a  brilliant  dark  steel- 
grey  lustre,  and  volatilises  before  it  melts,  at  a  temperature  of 
about  1 80°  C.  It  gives  off  a  colourless  vapour,  with  an  op- 
pressive garlic-like  smell.  If  heated  in  air,  it  combines  with 
oxygen,  and  becomes  converted  into  arsenious  anhydride, 
which  condenses  upon  somewhat  warm  surfaces  in  trans- 
parent brilliant  octahedra. 

Exp.  244. — Cut  off  with  a  triangular  file  the  portion  of  the 
tube  containing  the  mirror  of  arsenicum  obtained  in  the  last 
experiment.  Crush  the  glass  and  put  the  fragments  into  another 
sealed  quill  tube,  and  heat  the  broken  portions  gently:  the  metal 
will  be  sublimed,  but  will  combine  with  the  oxygen  of  the  air  in 
the  tube,  on  the  cool  sides  of  which,  by  the  aid  of  a  pocket  lens, 
octahedra  of  arsenious  anhydride  may  be  seen  condensed. 

Arsenicum  takes  fire  if  thrown  in  powder  into  chlorine  gas, 
and  it  combines  readily  with  bromine,  iodine,  and  sulphur, 
if  gently  heated  with  them.  Nitric  acid  oxidises  the  metal 
rapidly.  Hydrochloric  acid  has  but  little  action,  unless  a 
little  nitric  acid  or  nitre  be  added. 

Arsenicum  is  alloyed  in  small  quantity  with  lead,  to  facili- 
tate its  taking  a  globular  form  in  the  manufacture  of  shot. 
It  is  also  used  in  combination  with  copper  and  oxygen  in 
the  preparation  of  certain  green  pigments ;  and  orpiment, 


Tests  for  A  rsen  ic.  255 

which  is  a  yellow  largely  employed,  is  one  of  the  sulphides  of 
the  metal. 

Arsenicum  forms  two  compounds  with  oxygen  (As2O3  and 
As2O5),  both  of  which,  when  combined  with  water,  form 
acids. 

Arsenious  anhydride,  or  White  Arsenic  (As2O3),  is  obtained 
usually  as  an  opaque  milk-white  mass,  often  containing  small 
portions  or  layers  of  the  transparent  crystalline  form  of  the 
compound.  It  is  but  sparingly  soluble  in  cold  water,  but 
more  so  in  boiling  water,  and  still  more  readily  in  hydro- 
chloric acid.  Alkaline  solutions  dissolve  it  easily,  and  furnish 
a  solution  of  arsenite  of  the  metal,  which  does  not  crystallise. 
When  heated  to  about  190°  the  anhydride  softens,  and  sub- 
limes before  fusing.  Its  vapour  is  colourless,  extremely 
dense  (of  sp.  gr.  13*8),  and  it  contains  i  volume  of  the  vapour 
of  the  metal  and  3  of  oxygen  condensed  into  i  volume, 
being  double  the  density  that  its  composition  would  have 
led  us  to  expect. 

Exp.  245. — Boil  i  gram  of  arsenious  anhydride  with  3  of 
potassic  carbonate  in  100  c.  c.  of  water  till  it  is  dissolved,  and 
add  it  to  a  solution  of  3  grams  of  cupric  sulphate  in  100  c.  c.  of 
water:  a  beautiful  green  precipitate  of  Scheetes  Green  (CuHAsO-) 
will  be  obtained. 

Exp.  246. — Add  a  few  drops  of  a  solution  of  arsenious  anhy- 
dride to  200  or  300  c.  c.  of  water,  and  then  3  or  4  c.  c.  of  hydro- 
chloric acid;  place  in  the  liquid  two  or  three  slips  of  bright 
copper  foil,  and  boil  the  whole  for  a  few  minutes  :  the  copper 
foil  will  become  coated  with  a  steel-grey  -film.  Part  of  the 
copper  becomes  dissolved,  and  displaces  the  arsenicum,  which 
is  thrown  down  on  the  undissolved  portion.  Pour  off  the  water, 
dry  the  copper  on  blotting-paper,  and  heat  the  foil  in  a  quill 
tube,  sealed  at  one  end.  The  arsenicum  will  be  oxidized  and 
will  sublime,  condensing  in  minute  octahedra  on  the  cold  sides 
of  the  tube. 

This  is  Reinserts  test  for  arsenic.  Marsh's  test  may  be 
made  as  follows  : — 

Exp.  247. — Into  a  wide-mouthed  flask  of  the  capacity  of  150 


256 


Arsenic  Compounds. 


or  200  c.  c.,  fit  a  cork  provided  with  a  tube  funnel  passing 
nearly  to  the  bottom,  and  with  a  second  bent  tube,  which  may 
have  a  bulb  blown  upon  it,  as  shown  in  Fig.  71.  This  is  to  be 
connected  by  means  of  a  cork  with  a  wider  tube  loosely  filled 
with  calcic  chloride.  To  the  end  of  this  drying-tube  attach  a 
piece  of  quill  tube,  free  from  lead,  drawn  out  into  a  capillary 
end.  In  the  flask  place  a  few  fragments  of  pure  zinc,  or,  better 
still,  of  magnesium  foil.  Then  pour  on  some  water,  and  add 
a  sufficient  quantity  of  pure  sulphuric  acid  to  cause  a  steady 
Fig.  71. 


formation  of  hydrogen.  When  all  the  air  has  had  time  to  be 
displaced,  apply  the  flame  of  a  lamp  to  the  shoulder  or  begin- 
ning of  the  narrowed  part  of  the  tube.  Add  through  the  funnel 
two  or  three  drops  of  a  solution  of  arsenious  acid.  Immediate 
voltaic  action  will  occur ;  the  arsenious  acid  will  be  deprived  of 
its  oxygen,  and  part  of  the  metal  will  at  the  instant  combine 
with  hydrogen,  forming  arseniuretted  hydrogen.  This  gas  will 
be  separated  into  arsenicum  and  hydrogen  as  it  passes  through 
the  heated  tube,  and  the  metal  will  be  deposited  as  a  steel-grey 
ring  just  beyond  the  spot  at  which  the  heat  is  applied. 

Arsenic  Anhydride  (As2O5)  may  be  obtained  by  boiling 
arsenious  anhydride  with  nitric  acid,  and  evaporating  to  dry- 
ness.  It  is  very  soluble  in  water,  and  forms  a  powerful 
tribasic  acid,  which  furnishes  salts  ;  these  present  a  very  close 
resemblance  to  the  tribasic  phosphates.  When  united  with 
the  same  metal,  the  arseniate  and  phosphate  crystallise  in 


Arseniuretted  Hydrogen. 

exactly  the  same  form,  and  with  the  same  number  of  mole- 
cules of  water  of  crystallisation. 

The  hydric  disodic  arseniate  (Na2HAsO4,  i2H2O)  is  made 
in  large  quantity  for  the  calico  printer  and  dyer.  The  potassic 
dihydric  arseniate  (KH2AsO4)  crystallises  in  fine  octahedra, 
which  are  easily  obtained  by  throwing  a  mixture  of  equal 
parts  of  nitre  and  arsenious  anhydride  into  a  red-hot  clay 
crucible.  Allow  the  mass  to  cool,  dissolving  the  residue  in 
a  small  proportion  of  water,  and  setting  it  aside  to  crys- 
tallise. 

Arsenicum  and  sulphur  combine  in  several  proportions: 
the  red  compound  (As2S2)  is  called  realgar •;  orpiment  is 
As2S3;  and  there  is  another  sulphide,  As2S5;  these  two  last 
correspond  to  arsenious  and  arsenic  anhydride. 

Orpiment  is  easily  made  by  passing  sulphuretted  hydrogen 
through  a  dilute  solution  of  arsenious  acid  in  hydrochloric 
acid.  Orpiment  melts  easily  :  it  is  soluble  in  ammonia,  as 
well  as  in  potash  and  soda,  and  in  a  solution  of  an  alkaline 
sulphide. 

Only  one  compound  of  chlorine  and  arsenicum,  the  tri- 
chloride (AsCl3),  is  known.  It  is  liquid  and  volatile.  Corre- 
sponding compounds  with  bromine  and  iodine  are  solid. 

Arseniuretted  Hydrogen  (AsH3).  (Mol.  and  Atomic  Wt. 
78;  Sp.  Gr.  2-695;  Relative  Wt.  39;  Mol.  Vol.  |"T"1-)— 
Arsenicum  forms  a  remarkable  gaseous  compound  with 
hydrogen,  which  is  a  deadly  poison.  It  is  neither  acid  nor 
alkaline,  but  it  has  a  close  analogy  with  phosphuretted 
hydrogen,  and  with  ammonia.  It  is  nearly  insoluble  in 
water,  but  is  absorbed  with  decomposition  by  solutions 
of  cupric  sulphate,  of  corrosive  sublimate,  and  of  argentic 
nitrate.  In  the  last  case,  metallic  silver  and  arsenic  acid  are 
formed — 

AsH3  +  8AgNO3  +  4H2O  =  8HNO3  +  H3AsO4  +  4Ag2. 

Its  decomposition,  when  heated,  is  turned  to  account  in 
Marsh's  test  for  arsenic. 


258  Antimony. 

(58)  ANTIMONY:  Symb.  Sb ;  Atom.  Wt.  122;  Sp.  Gr. 
671 ;  Eusing  Pt.  about  450°. 

This  metal  is  always  extracted  from  the  sesquisulphide, 
which  is  a  bluish-white  lustrous  mineral,  crystallised  in  four- 
sided  prisms,  striated  across  their  length.  This  sulphide 
is  brittle,  and  melts  below  a  red  heat,  crystallising  as  it  cools. 
The  crude  antimony  of  commerce  is  the  sulphide  freed  by 
fusion  from  its  earthy  impurities.  The  metal  is  easily  ob- 
tained in  small  quantities  by  mixing  4  parts  of  this  sulphide 
with  2  of  pearlash  and  \\  nitre,  powdering  and  mixing  them 
intimately,  and  throwing  the  powder  in  small  portions  at  a 
time  into  a  crucible  kept  at  a  bright  red  heat.  The  quan- 
tity of  nitre  used  is  not  sufficient  to  oxidise  both  the  sul- 
phur and  the  metal ;  and  as  the  sulphur  is  the  more  com 
bustible  element,  it  burns,  while  the  metal  melts,  and  collects 
beneath  the  melted  slag  of  potassic  sulphate. 

Antimony  is  a  brilliant  bluish- white  metal,  crystallising  in 
plates,  and  is  so  brittle  that  it  may  be  easily  powdered  in  a 
mortar. 

It  melts  just  above  a  red  heat,  and  burns  brilliantly  in  a 
current  of  air,  giving  off  white  fumes,  composed  chiefly  of 
antimonious  oxide.  Powdered  antimony  takes  fire  when 
thrown  cold  into  chlorine  gas,  and  it  combines  energetically 
both  with  bromine  and  with  iodine.  Nitric  acid  and  aqua 
regia  oxidize  it  with  violence;  and  if  powdered,  and  boiled 
with  sulphuric  acid,  it  is  converted  into  a  sulphate.  The 
metal,  in  fine  powder,  digested  with  a  persulphide  of  one  of 
the  alkali  metals,  is  dissolved. 

Antimony  is  too  brittle  to  be  used  alone,  but  it  is  useful 
for  hardening  other  metals  when  alloyed  with  them.  Type 
metal  is  an  alloy  of  lead  with  about  one-fourth  of  antimony, 
and  often  about  the  same  quantity  of  tin  is  added. 

The  oxide,  when  ground  up  with  linseed  oil,  furnishes  a 
white  pigment,  inferior,  however,  to  common  white  lead; 
and  tartar  emetic,  a  salt  of  tartaric  acid  with  potassium  and 
antimony  2[K(SbO)C4H4O6]H2O,  is  a  very  active  medicine. 


Compounds  of  Antimony.  259 

Antimony  forms  three  oxides  :  Sb2O3,  the  sesquioxide,  is  a 
feeble  base,  which  is  freely  soluble  in  hydrochloric  and  in 
tartaric  acid;  Sb2O5  is  a  metallic  anhydride  ;  it  furnishes 
salts  with  bases  called  antimoniates  ;  and  Sb2O4  is  a  com- 
pound of  these  two,  which  is  formed  by  heating  either  of  the 
other  oxides  in  a  current  of  air. 

Antimony  combines  with  hydrogen,  and  forms  a  colourless 
gas,  much  resembling  arseniuretted  hydrogen,  but  with  no 
special  odour.  It  may  be  obtained  by  dissolving  an  alloy  of 
zinc  and  antimony  in  diluted  sulphuric  acid.  When  a  solu- 
tion of  any  antimonious  salt  is  added  to  a  mixture  of  zinc 
and  sulphuric  acid  which  is  giving  off  hydrogen,  the  antimonial 
salt  is  decomposed,  and  antimoniuretted  hydrogen  comes  off 
mixed  with  the  free  hydrogen.  It  is  decomposed  when 
passed  through  a  red-hot  tube,  and  a  brilliant  crust  of  me- 
tallic antimony  is  deposited.  When  the  gas  is  burned  in 
the  air,  white  clouds  of  antimonious  oxide  are  formed. 

Antimony  forms  two  sulphides  (Sb2S3  and  Sb2S5),  which 
correspond  to  the  two  principal  oxides.  They  are  both 
soluble  in  the  solutions  of  the  sulphides  of  the  alkali  metals, 
and  combine  with  them  to  form  definite  crystalline  com- 
pounds, or  sulphur  salts. 

The  sesquisulphide  (Sb2S3)  is  the  ore  of  the  metal,  but  it 
may  also  be  obtained  artificially  in  beautiful  orange-coloured 
flocculi,  by  sending  a  current  of  sulphuretted  hydrogen 
through  a  solution  of  tartar  emetic,  or  other  soluble  antimo- 
nious salt.  The  formation  of  this  compound  furnishes  one 
of  the  best  tests  for  antimony.  It  is  soluble  with  escape  of 
sulphuretted  hydrogen  in  hot  hydrochloric  acid. 

The  metal  forms  two  chlorides  (SbCl3  and  SbCl5),  which 
correspond  to  the  oxides  and  sulphides.  The  trichloride 
(SbCl3)  is  a  fusible  solid,  which  is  a  strong  caustic.  It  is 
soluble  in  hydrochloric  acid ;  but,  on  dilution,  unless  the 
quantity  of  acid  be  very  large,  an  insoluble  oxy chloride 
(SbCl3,  Sb2O3)  falls  as  a  white  powder,  readily  soluble  in 
tartaric  acid.  If  antimony  is  heated  with  chlorine  in  excess, 

S  2 


260  Oxides  of  Bismuth. 

it  forms  the  pentachloride  (SbCl5),  a  fuming  volatile  liquid, 
which  is  decomposed  by  a  large  quantity  of  water. 

The  compounds  of  antimony  are  powerful  irritant  poisons. 
Antimony  is  more  likely  to  be  mistaken  for  arsenic  than  for 
any  other  metal.  The  crust  which  is  formed  by  decom- 
posing antimoniuretted  hydrogen  in  Marsh's  apparatus  does 
not  yield  octahedra,  when  sublimed  in  a  tube  with  air,  but 
prisms.  The  metal  is  also  easily  soluble  in  yellow  ammo- 
nium sulphide,  which  is  nearly  without  effect  upon  arsenical 
crusts. 

(59)  BISMUTH:  Symb.  Bi;  Atom.  Wt.  210;  Sp.  Gr.  9-8; 
Fusing  Pt.  264°. 

This  metal  is  found  but  rarely,  and  is  generally  met  with 
in  the  native  state  in  quartz  rock,  from  which  it  is  commonly 
separated  by  simple  fusion.  It  is  hard,  brittle,  and  of  a 
reddish-white  colour.  It  may  be  crystallised  more  readily 
than  any  other  metal ;  and  it  furnishes  large  hollow  cubes 
by  fusion  and  slow  cooling,  pouring  off  the  inner  part  before 
the  whole  has  become  solid.  Bismuth  does  not  become 
tarnished  by  exposure  to  the  air  at  ordinary  temperatures, 
but  it  is  rapidly  oxidized  in  a  current  of  air  at  a  red  heat. 
If  thrown  in  powder  into  chlorine  gas,  it  takes  fire ;  and  it 
combines  easily  with  bromine,  iodine,  and  sulphur.  Nitric 
acid  is  its  best  solvent.  The  nitrate  crystallises  in  flat,  trans- 
parent, colourless  prisms. 

This  metal  is  not  used  alone,  but  it  enters  into  a  remark- 
ably fusible  alloy,  which  may  be  prepared  by  melting  to- 
gether 2  parts  of  bismuth,  i  of  lead,  and  i  of  tin.  This 
mixture  melts  at  a  little  below  ioo°C.;  and  as  it  expands  in 
setting,  it  is  valuable  to  the  die-sinker,  as  it  enables  him 
to  take  sharp  and  faithful  impressions  of  his  work  from  time 
to  time  during  its  progress.  Bismuth  forms  two  principal 
oxides:  Bi2O3,  which  is  basic,  and  is  easily  obtained  by 
heating  the  nitrate  to  low  redness  ;  it  is  yellow,  fuses  at  a 
red  heat,  and  may  be  obtained  as  a  white  hydrate  by 


Copper.  261 

adding  ammonia  to  a  solution  of  one  of  the  bismuth  salts  ; 
the  other  oxide  (Bi2O5)  is  brown,  and  furnishes  unstable 
compounds  with  bases. 

A  native  sulphide  (Bi2S3)  is  occasionally  found  crystallised 
in  needles,  and  is  formed  as  a  black  precipitate  when  solu- 
tions of  the  metal  are  treated  with  sulphuretted  hydrogen. 

A  trichloride  (BiCl3)  may  be  obtained  as  a  very  fusible, 
volatile,  and  deliquescent  substance.     It  is  decomposed  by 
water,  and  a  white  oxychloride  is  formed,  while  ^hydrochloric 
.  acid  is  set  free. 

BiCl3  +  H2O     =     BiOCl  -f   2HC1. 

The  Nitrate  (Bi3NO3,  5H2O)  is  the  most  important  solu- 
ble salt  of  this  metal.     It  is  soluble  in  excess  of  acid,  but  if 
largely  diluted  with  water  a  white  basic  nitrate  (Bi2O3,  2HNO3) 
is  precipitated,  while  an  acid  salt  is  formed  in  the  liquid — 
3(Bi3NO3)    +   3H,O     =     Bi2O3,  2HNO3   +    Bi3NO3,  4HNO3. 

Bismuth  salts  generally  become  milky  when  their  solutions 
are  diluted  with  water,  owing  to  the  formation  of  an  in- 
soluble salt  containing  excess  of  the  oxide.  This  precipi- 
tate is  easily  dissolved  by  acetic  acid.  Solutions  of  the 
alkalies  give  a  precipitate  of  the  white  hydrated  oxide,  not 
soluble  in  excess  of  the  alkali.  Solutions  of  the  carbonates 
and  phosphates  give  a  white  precipitate  with  bismuth  salts ; 
but  the  yellow,  with  potassic  chromate,  insoluble  in  caustic 
potash,  is  used  to  distinguish  bismuth  from  lead,  as  the  lead 
chromate  is  dissolved  by  excess  of  potash.  Before  the  blow- 
pipe bismuth  salts  on  charcoal  yield  a  brittle  bead  of  metal, 
surrounded  by  a  ring  of  yellow  oxide. 


CHAPTER  XVI. 

I.    COPPER.       2.    LEAD.       3.    THALLIUM. 

(60)  i.  COPPER:  Symb.  CM;  Atom.  Wt.  63-5.  — This 
valuable  metal  is  frequently  found  native,  but  its  most 
common  ore  is  the  sulphide  of  copper  and  iron,  known  as 


Properties  of  Copper. 

copper  pyrites  (Cu2S,  Fe2S3) ;  and  other  less  common  ores  are 
the  green  carbonate,  malachite  (CuCO3,  CuO,  H2O),  and  the 
blue  carbonate  (2CuCO3,  CuO,  H2O). 

In  the  Welsh  process  of  copper  smelting,  the  pyrites  is 
roasted  at  a  dull  red  heat,  to  get  rid  of  portions  of  the  sul- 
phur. The  calcined  ore  is  then  melted  with  a  siliceous  slag, 
which  removes  the  iron  in  the  form  of  silicate  of  the  oxide, 
leaving  the  copper  in  the  condition  of  a  heavy  fusible  sub- 
sulphide.  This  is  separated  from  the  slag,  which  floats 
above  it,  and  is  then  roasted,  so  as  partly  to  get  rid  of  the 
sulphur  as  sulphurous  anhydride,  and  partly  to  convert  the 
copper  into  oxide.  When  this  point  is  reached,  the  smelter 
stirs  in  this  oxide,  and  mixes  it  with  undecomposed  cupreous 
sulphide.  The  copper,  both  from  the  oxide  and  the  sulphide, 
then  becomes  reduced  to  the  metallic  state,  and  the  sulphur 
and  oxygen  pass  off  together  as  sulphurous  anhydride — 

Cu2S   +   2CuO    =    4Cu   +   SO2. 

The  crude  or  blistered  copper  thus  obtained  is  then  melted 
in  large  quantities  in  a  reverberatory  furnace,  where  it  is 
poled \  that  is  to  say,  the  trunk  of  a  young  tree  is  thrust  into 
the  melted  metal,  and  thus  the  last  portions  of  oxide  are 
reduced  to  the  metallic  state  by  the  combustible  gases  given 
off  by  the  wood,  and  the  copper  is  brought  into  the  pure  and 
tough  condition  in  which  it  is  required  for  use. 

Copper  is  a  tough,  tenacious,  and  somewhat  hard  metal, 
with  a  well-known  red  colour.  It  emits  a  peculiar  odour 
when  rubbed.  It  may  be  drawn  into  very  fine  wire,  can  be 
rolled  into  foil,  and  hammered  into  leaf.  It  is  an  excellent 
conductor  of  electricity  and  of  heat.  When  required  in  a 
state  of  perfect  purity,  it  may  readily  be  deposited  in  sheets 
from  a  solution  of  its  sulphate  by  the  current  from  one  or 
two  cells  of  the  voltaic  battery.  It  tarnishes  when  exposed 
to  the  atmosphere  ;  and  if  heated  to  redness  in  the  air,  a  layer 
of  oxide  is  formed  upon  the  surface,  which  scales  off  if  it  be 
suddenly  quenched  in  water,  leaving  the  metal  bright  beneath. 


Oxides  of  Copper.  263 

Nitric  acid  dissolves  copper  with  violence,  giving  off  red 
fumes  of  nitrous  anhydride.  Sulphuric  acid  in  the  cold  does 
not  attack  the  metal ;  but  if  the  strong  acid  be  boiled  upon 
it,  the  copper  is  dissolved,  cupric  sulphate  is  formed,  and 
sulphurous  anhydride  is  set  free. 

Copper  melts  at  a  bright  red  heat,  or  1090°  C.  It  is 
extensively  used  in  the  manufacture  of  boilers,  kettles, 
saucepans,  and  the  like ;  also  for  the  sheathing  of  ships ;  and 
it  enters  into  the  formation  of  many  useful  alloys,  brass 
being  a  mixture  of  about  2  parts  of  copper  and  i  of  zinc, 
and  bell  metal  and  bronze,  which  are  alloys  of  copper  and 
tin.  Some  of  the  compounds  of  copper  are  used  as  pigments. 

There  are  two  oxides  of  copper  :  the  red,  or  cupreous, 
oxide  (Cu2O),  and  the  black,  or  cupric,  oxide  (CuO).  It  is 
the  latter  which  furnishes  the  important  salts  of  the  metal. 
The  hydrated  red  oxide  is  easily  obtained  by  dissolving  i 
part  of  cupric  sulphate  and  i  of  grape-sugar  in  water,  adding 
a  solution  of  potash  till  the  precipitate  of  hydrated  cupric 
oxide  is  redissolved,  and  then  boiling  the  solution.  A  crys- 
talline precipitate  of  cupreous  oxide  is  deposited.  This 
oxide  is  used  for  colouring  glass  of  a  ruby  red. 

Cupreous  oxide  is  soluble  in  ammonia,  and  forms  a 
colourless  liquid,  which  turns  blue  directly  that  it  is  exposed 
to  the  action  of  oxygen. 

Exp.  248. — To  a  solution  of  cupric  sulphate  add  ammonia 
in  excess;  introduce  the  solution  into  a  bottle  with  some 
copper  turnings.  Cork  up  the  bottle  securely,  and  place  it 
in  water ;  heat  it  for  some  hours  nearly  to  boiling.  The  blue 
solution  will  gradually  become  colourless,  and  a  portion  of 
the  copper  will  be  dissolved,  the  cupric  becoming  converted 
into  cupreous  oxide.  When  cold,  pour  a  little  of  the  colour- 
less liquid  upon  a  white  plate  :  it  will  absorb  oxygen  instantly, 
and  will  become  blue. 

Cupric  oxide  (CuO)  may  be  best  obtained  pure  by  dis- 
solving pure  copper  in  nitric  acid,  evaporating  the  blue 
solution  to  dryness,  and  decomposing  the  nitrate  by  heating 


264  Tests  for  Copper. 

it  to  redness  in  a  clay  crucible  for  a  considerable  time. 
Nitrogen  and  oxygen  are  expelled,  and  cupric  oxide  is  left 
as  a  black  powder.  It  is  soluble  in  acids,  and  furnishes  the 
blue  and  green  salts  of  the  metal.  A  solution  of  any  one 
of  these  salts,  such  as  the  sulphate,  when  decomposed  by 
potash,  gives  a  pale  blue  hydrated  cupric  oxide,  which,  when 
boiled  in  water,  becomes  black  and  anhydrous.  Ammonia 
gives  a  similar  precipitate,  which  is  redissolved  by  an  excess 
of  the  alkali,  furnishing  an  intensely  blue  liquid,  charac- 
teristic of  copper. 

The  sulphate,  or  blue  vitriol  (CuSO4,  5H2O),  is  its  most 
important  salt.  It  is  easily  obtained  on  the  large  scale  by 
boiling  metallic  copper  with  oil  of  vitriol  diluted  with  half 
its  bulk  of  water.  It  crystallises  in  beautiful  blue  prisms, 
which,  when  heated,  lose  water,  and  crumble  down  to  a 
white  powder. 

Cupric  chloride  (CuCl2,  2H2O)  may  be  obtained  by  dis- 
solving the  carbonate  or  the  oxide  in  hydrochloric  acid,  and 
evaporating.  Its  crystals  are  green,  and  form  a  green  solu- 
tion, which  becomes  blue  on  dilution.  When  heated,  it 
loses  water,  and  then  half  its  chlorine,  cupreous  chloride 
(CuCl)  being  formed.  Cupreous  chloride  is  also  formed  when 
a  solution  of  cupric  chloride  in  hydrochloric  acid  is  digested 
on  copper  in  closed  vessels  ;  it  crystallises  gradually  in 
transparent  tetrahedra,  insoluble  in  water,  but  soluble  in 
excess  of  hydrochloric  acid. 

Cupreous  sulphide  (Cu2S)  is  occasionally  found  native,  as 
is  also  the  cupric  sulphide  (CuS),  which  is  precipitated  as  a 
brownish-black  hydrate  when  a  solution  of  a  cupric  salt  is 
exposed  to  the  action  of  sulphuretted  hydrogen. 

Tests  for  Copper. — In  addition  to  the  characteristic  blue 
liquid  formed  in  solutions  of  cupric  salts  by  the  addition  of 
excess  of  ammonia,  they  are  known  by  their  forming  a  brown 
precipitate  with  potassic  ferrocyanide,  and  by  the  deposit 
of  metallic  copper  which  is  produced  on  a  polished  plate  of 
iron,  if  plunged  into  a  feebly  acid  solution  of  a  cupric  salt. 


Properties  of  Lead.  26$ 

Before  the  blowpipe,  on  charcoal  in  the  reducing  flame,  com- 
pounds of  copper  furnish  a  red  malleable  bead  of  the  metal. 

Copper  salts  produce  vomiting  when  swallowed,  and  act 
as  powerful  irritant  poisons. 

(61)  2.  LEAD:  Symb.  Pb;  Atom.  Wt.  207. — This  useful 
metal  occurs  tolerably  abundantly  in  the  form  of  sulphide, 
or  galena  (PbS),  which  is  its  only  ore  of  importance,  although 
it  is  found  both  as  carbonate  and  as  sulphate,  and  in  one  or 
two  other  minerals. 

In  extracting  the  metal  the  sulphide  is  roasted  on  the 
hearth  of  a  reverberatory  furnace.  Sulphur  burns  off,  and 
a  mixture  of  oxide  and  sulphate  of  lead  is  formed.  These 
substances  are  at  intervals  stirred  by  the  workman  into  the 
melted  mass  of  sulphide  beneath.  The  oxide  and  sulphate, 
as  well  as  the  sulphide,  give  up  their  lead  in  the  metallic 
state,  and  the  sulphur  and  oxygen  pass  off  as  sulphurous 
anhydride.  Galena  yields  by  oxidation — 

2PbS       +     30,     =     2PbO      +      2SO2;  and 

PbS        +     2O2     -       PbSO4  ;  and  then 

2PbO       +     PbS    =     sPb         +        SO2;  while 
PbSO4   +     PbS    =     2Pb         +      2SOa. 

Lead  is  a  soft,  bluish- white,  brilliant  metal,  of  little  tena- 
city. It  melts  at  a  temperature  of  325°  C.,  and  may  with 
some  difficulty  be  crystallised  by  slow  cooling.  It  shrinks 
as  it  becomes  solid,  and  hence  is  not  well  fitted  for  castings. 
If  exposed  to  a  damp  atmosphere  it  soon  tarnishes,  and  an 
adherent  layer  of  oxide  forms  upon  the  surface.  If  heated 
in  a  current  of  air,  when  melted,  the  metal  oxidises  quickly, 
and  furnishes  an  oxide,  which  melts  at  a  full  red  heat. 
During  this  operation  it  emits  white  fumes,  owing  to  a 
partial  volatilisation  at  a  high  temperature.  Nitric  acid, 
when  somewhat  diluted,  dissolves  the  metal  rapidly,  but 
sulphuric  and  hydrochloric  acids  have  but  little  effect  upon 
it.  It  is  on  this  account  that  sulphuric  acid  is  made  in 
chambers  lined  with  lead 


266  Oxides  of  Lead. 

Lead  is  extensively  used  in  the  construction  of  cisterns, 
gutters,  and  pipes  for  the  storage  and  distribution  of  water ; 
also  for  roofing.  It  enters  into  many  valuable  alloys,  such 
as  pewter,  type-metal,  and  plumbers'  solder ;  and  is  used 
in  the  form  of  oxide  in  making  glass.  The  carbonate,  oxy- 
chloride,  and  chromate  are  largely  employed  as  pigments. 

Lead  is  a  dangerous  but  insidious  poison,  producing 
symptoms  of  colic  and  partial  palsy.  It  is  apt  to  accumu- 
late in  the  body  when  swallowed  in  minute  quantities ;  and 
as  it  is  largely  used  in  the  storage  of  water,  it  is  important  to 
study  the  conditions  under  which  lead  is  liable  to  be  che- 
mically acted  on. 

When  lead  is  exposed  to  a  dry  air  it  does  not  alter,  but 
pure  water  in  the  presence  of  air  corrodes  it  rapidly.  The  lead 
becomes  oxidized  on  the  surface;  the  water  dissolves  the 
oxide  slightly,  and  this  solution  absorbs  carbonic  acid  :  an  in- 
soluble hydrated  basic  carbonate  of  lead  is  precipitated,  fresn 
oxide  is  formed  on  the  metal,  is  dissolved  by  the  water,  fresh 
carbonic  acid  is  absorbed,  a  fresh  precipitate  is  formed;  and 
so  the  process  goes  on  continuously.  The  presence  in  the 
water  of  small  quantities  of  many  soluble  salts,  such  as  from  30 
to  60  mgms.  per  litre,  materially  alter  this  result.  The  corro 
sion  is  much  increased  by  the  presence  of  chlorides,  nitrates, 
and  nitrites ;  but  it  is  diminished  by  the  sulphates,  phosphates, 
and  especially  by  the  carbonates.  Lead  oxide  is  scarcely  so- 
luble in  water  which  contains  these  salts.  The  water  supplied 
in  towns  generally  holds  sufficient  calcic  carbonate  dissolved 
to  prevent  it  from  acting  to  any  injurious  extent  upon  the 
metal.  A  film  of  insoluble  basic  carbonate  is  formed  upon 
the  surface,  and  thus  the  lead  beneath  is  protected  from 
further  corrosion.  Sometimes,  as  in  the  pure  lake  waters  of 
Scotland,  the  presence  of  a  little  vegetable  matter  acts  as  a 
preservative,  by  combining  with  the  oxide  of  lead,  and 
forming  an  insoluble  lining  to  the  cisterns  and  pipes.  Slate 
cisterns,  however,  are  in  all  cases  to  be  preferred. 

Lea.d  forms  four  oxides  :    a  black  suboxide  (Pb2O) ;   a 


Compounds  of  Lead.  267 

protoxide,  the  important  base  (PbO)  from  which  the  salts  of 
the  metal  are  derived;  a  brown  dioxide  (PbO2),  which  is  in- 
soluble in  the  acids ;  and  an  intermediate  oxide  (red  lead), 
a  compound  of  one  or  of  two  molecules  of  the  protoxide 
with  one  of  the  peroxide  (PbO,  PbO2,  or  more  usually 
2PbO,  Pb02). 

The  protoxide,  or  litharge  (PbO),  is  commonly  obtained,  by 
heating  the  metal  in  a  current  of  air,  as  a  pale  yellow  scaly 
mass.  It  fuses  at  a  full  red  heat,  and  is  a  valuable  flux  to 
the  assayer;  but  it  speedily  penetrates  and  destroys  the 
crucibles  in  which  it  is  melted.  A  solution  of  a  salt  of  lead, 
such  as  plumbic  nitrate,  furnishes,  on  the  cautious  addition 
of  potash  or  soda,  a  white  precipitate  of  the  hydrated  oxide; 
it  is  soluble  in  excess  of  the  alkali.  Lead  oxide  is  a  power- 
ful base.  It  is  readily  soluble  in  the  acids,  and  has  a  strong 
tendency  to  form  salts  which  contain  an  excess  of  base. 

Exp.  249. — Dissolve  2  or  3  grams  of  lead  acetate  in  200  or 
300  c.  c.  of  water,  and  boil  it  with  a  gram  of  finely-powdered 
litharge  :  the  oxide  will  gradually  be  dissolved,  and  the  solu- 
tion will  restore  the  blue  colour  to  reddened  litmus. 

Exp.  250. — Blow  a  little  air  from  the  lungs  through  a  short 
quill  tube  into  a  little  of  the  solution  in  a  test-tube  :  the  solu- 
tion will  become  filled  with  white  silky  scales  of  the  hydrated 
oxycarbonate  of  lead  (PbO,  H2O,  PbCO3). 

This  solution  consequently  furnishes  one  of  the  best  tests 
for  un combined  carbonic  anhydride,  whether  in  air  or  in  water. 

Red  lead,  or  minium,  is  obtained  by  heating  metallic  lead 
in  a  current  of  air  below  the  point  at  which  the  litharge 
fuses.  The  oxide  is  ground  with  water  to  a  fine  powder, 
and  the  fine  particles,  after  they  have  settled  down  from 
suspension  in  water,  are  heated  to  about  320°  C.,  in  iron 
trays,  in  a  current  of  air  for  several  hours.  The  oxygen 
is  slowly  absorbed,  and  a  fine  red  crystalline  powder  is 
obtained.  If  heated  to  redness,  the  absorbed  oxygen  is 
driven  off,  and  litharge  is  left.  Red  lead  is  largely  used  in 
making  flint  glass. 


268  Salts  of  Lead. 

Exp.  251. — Pour  a  little  nitric  acid,  diluted  with  3  or  4 
times  its  bulk  of  water,  upon  a  few  decigrams  of  red  lead  : 
the  red  colour  will  disappear,  and  the  brown  dioxide  (PbO3) 
will  be  left  undissolved,  whilst  lead  nitrate  is  formed. 

Lead  Sttlphide  (PbS). — Lead  has  a  very  powerful  attrac- 
tion for  sulphur.  Galena,  the  common  ore  of  the  metal, 
is  the  sulphide  ;  it  has  a  deep  leaden  colour,  is  hard,  brittle, 
and  has  a  high  metallic  lustre.  It  fuses  at  a  full  red  heat, 
and  is  oxidized  easily,  with  escape  of  sulphurous  anhydride, 
in  a  current  of  air. 

Exp.  252. — Mix  10  grams  of  powdered  galena  with  14  of 
dried  sodic  carbonate  and  I  gram  of  powdered  charcoal. 
Place  3  or  4  blacksmith's  nails,  with  their  heads  downwards, 
in  a  Cornish  clay  crucible;  then  add  the  mixture.  Cover  it 
with  a  thin  layer  of  fused  and  powdered  borax.  Heat  the 
crucible  to  full  redness  for  10  minutes;  take  out  the  nails. 
When  cool,  break  the  crucible :  a  button  of  lead  will  be  found 
at  the  bottom,  sulphide  of  iron  being  formed,  while  metallic 
lead  separates.  This  method  is  commonly  used  in  the  dry 
assay  of  a  sample  of  galena. 

All  the  salts  of  lead,  both  soluble  and  insoluble,  become 
blackened  when  placed  in  water  containing  sulphuretted 
hydrogen. 

Lead  Chloride  (PbCl2)  is  sparingly  soluble;  it  is  preci- 
pitated in  crystalline  needles  on  adding  hydrochloric  acid  to 
a  solution  of  a  lead  salt. 

Lead  Sulphate  (PbSO4)  is  a  white  insoluble  powder  pro- 
duced on  adding  sodic  sulphate  or  other  soluble  sulphate  to 
a  solution  of  a  lead  salt. 

Lead  Iodide  (PbI2)  is  yellow  and  insoluble.  It  is  formed 
by  adding  potassic  iodide  to  a  soluble  lead  salt.  The 
Chromate  (PbCrO4)  is  also  yellow  and  insoluble. 

Lead  Nitrate  (Pt>2NO3)  is  prepared  by  dissolving  metallic 
lead  in  nitric  acid,  and  evaporating ;  octahedral  white  anhy- 
drous crystals  are  deposited.  Several  basic  nitrates  and 
nitrites  may  be  formed. 

Lead  Carbonate  (PbCO3),  or  white  lead,  is  one  of  the  most 


Thallium.  269 

important  insoluble  compounds  of  the  metal.  When  ground 
into  a  paste  with  a  drying  oil  (linseed  oil  being  generally 
used),  it  forms  the  basis  of  our  common  house  paints. 

Lead  forms  a  very  large  number  of  insoluble  compounds. 
The  sulphate,  iodide,  chromate,  and  sulphide  are  often 
used  as  tests  of  the  metal.  If  a  water  contain  lead,  even  in 
minute  quantity,  its  presence  is  easily  ascertained  by  taking 
two  similar  jars  of  25  cm.  high,  of  colourless  glass,  filling 
both  of  them  with  the  water,  and  adding  to  one  of  the  jars 
3  or  4  c.  c.  of  a  solution  of  sulphuretted  hydrogen.  A 
quantity  of  lead  less  than  one  part  in  two  millions  is  easily 
perceived,  by  the  brown  tinge  occasioned,  on  looking  down 
upon  a  sheet  of  white  paper ;  the  jar  to  which  the  test  has 
not  been  added  serving  as  a  standard  of  comparison. 

Exp.  253. — Dissolve  30  grams  of  lead  acetate  in  a  litre  of 
distilled  water  in  a  flask,  and  hang  up  in  the  solution  a  lump 
of  zinc.  If  the  glass  is  left  undisturbed  for  three  or  four  days, 
beautiful  crystalline  plates  of  lead,  forming  what  is  often  called 
the  l  lead  tree/  will  be  deposited  upon  the  zinc.  Zinc  will  have 
been  dissolved,  while  the  lead,  which  has  a  smaller  attraction  for 
the  radical  of  the  acid,  is  separated. 

Before  the  blowpipe  on  charcoal  the  salts  of  lead  yield  a 
soft,  white,  malleable  bead  of  the  metal,  surrounded  by  a 
yellow  ring  of  oxide. 

(62)  3.  THALLIUM:  Symb.  Tl;  Atom.  Wt.  204.— This 
is  a  metal  which  accompanies  certain  kinds  of  pyrites  in 
small  quantity.  It  was  discovered  quite  recently  by  the 
beautiful  green  colour  which  it  gives  to  flame  ;  and  this, 
when  viewed  by  the  spectroscope,  is  found  to  be  concen- 
trated into  a  single  intense  green  line.  It  is  a  heavy  metal, 
resembling  lead  in  appearance,  but  it  quickly  tarnishes  in 
the  air.  Its  principal  oxide  is  soluble  in  water,  and  has  an 
alkaline  reaction  on  red  litmus.  The  sulphate,  nitrate, 
and  carbonate,  are  white  soluble  salts.  The  sulphide  is 
brownish-black  ;  the  chloride  yellowish-white,  and  sparingly 
soluble. 


270 
CHAPTER  XVII. 

THE     NOBLE     METALS. 

i.  MERCURY.   2.  SILVER.   3.  GOLD.   4.  PLATINUM.   5.  PALLADIUM. 
6.  RHODIUM.    7.  OSMIUM.    8.  IRIDIUM.    9.  RUTHENIUM. 

(63)  i.  MERCURY  :  Symb.  Hg  ;  Atom.  Wt.  200  ;  Sf.  Gr. 
at  o°,  13*596;  of  Vapour,  6*976  ;  Melting  Pt.  —  39°  ;  Boiling 
Pt.  350°;  Atom.  andMol.  Vol.  [""T"| ;  *  Rel.  Wt.  100. 

This  remarkable  and  interesting  metal,  often  called  quick- 
silver, is  the  only  one  that  is  liquid  at  common  temperatures. 
It  is  found  in  but  few  places,  and  then  usually  as  sulphide 
in  the  red  ore  known  as  cinnabar,  accompanied  by  small 
quantities  of  the  metal  itself.  It  is  extracted  from  this  ore 
by  simply  roasting  it  in  a  current  of  air,  and  passing  the 
vapours  through  long  earthen  pipes.  The  mercury  condenses, 
and  the  sulphurous  anhydride  passes  off  into  the  air.  Mer- 
cury possesses  a  lustre  like  that  of  polished  silver.  It 
volatilises  slowly  at  all  temperatures  above  4°  C.  ;  and  when 
heated,  it  boils  at  350°,  giving  off  a  heavy  transparent 
vapour,  which  is  100  times  as  dense  as  hydrogen.  It  freezes 
at  —39°,  and  forms  a  white  malleable  mass,  which  contracts 
suddenly  as  it  becomes  solid.  When  pure,  it  is  not  tarnished 
by  exposure  to  the  air;  but  if  kept  at  a  temperature  of  300° 
or  400°,  it  absorbs  oxygen  slowly,  and  becomes  converted 
into  crystalline  scales  of  the  red  oxide.  The  purity  of  the 
metal  may  be  judged  of  by  the  perfect  mobility  and  spheri- 
city of  its  globules,  which  do  not  wet  non-metallic  surfaces. 
If  any  other  metals,  such  as  zinc,  lead,  or  bismuth,  be 
present,  the  globules  assume  an  irregular  elliptical  form, 
and  have  a  tail-like  prolongation  as  they  roll  about. 

Exp.  254. — Dissolve  a  fragment  of  lead  of  about  the  size  of  a 
mustard  seed  in  40  or  50  grams  of  clean  mercury.  Cork  it  up 
in  a  glass  bottle  which  will  hold  200  or  300  c.  c.  and  agitate  the 

*  The  molecule  of  the  vapour  of  mercury,  like  that  of  zinc,  cadmium, 
and  other  metallic  dyads,  contains  only  i  atom  of  the  metal. 


Properties  of  Mercury.  271 

mercury  briskly  :  a  black  film  will  be  found  over  the  surface. 
Withdraw  the  cork,  blow  out  the  air  with  a  pair  of  bellows,  and 
then  renew  the  shaking.  Repeat  this  three  or  four  times  until 
the  black  powder  ceases  to  increase.  Then  pour  the  mercury 
into  a  cone  of  writing-paper  folded  like  an  ordinary  filter,  but 
pierced  at  the  point  with  a  pin-hole,  and  supported  in  a  funnel : 
the  metal  will  run  through,  and  leave  the  oxide  of  lead,  mixed 
with  finely  divided  mercury,  adhering  to  the  paper.  If  a  little 
finely-powdered  loaf-sugar  be  added  before  agitating  the  mercury, 
the  process  is  effected  more  quickly. 

If  a  large  quantity  of  mercury  is  to  be  purified  from 
foreign  metals,  it  is  best  to  place  it  in  a  shallow  layer  on  the 
bottom  of  a  dish,  and  to  cover  it  with  nitric  acid  diluted 
with  ten  or  twelve  times  its  bulk  of  water,  leaving  it  for  a 
few  days  at  ordinary  temperatures,  frequently  stirring  the 
acid  and  mercury  together ;  after  which  it  may  be  washed, 
and  dried  with  a  cloth. 

Mercury  is  attacked  immediately  by  chlorine  and  by  bro- 
mine ;  more  slowly  by  iodine.  It  also  dissolves  most  of  the 
metals,  except  iron  and  platinum.  Gold,  silver,  and  tin 
amalgams  are  used  in  the  arts.  It  also  combines  readily 
with  lead,  bismuth,  antimony,  zinc,  and  copper.  The 
amalgamation  is  immediately  effected  by  cleansing  the  sur- 
face of  the  metal  with  a  solution  of  mercury  in  nitric  acid, 
and  then  placing  the  metal  in  the  mercury. 

Nitric  acid   dissolves   mercury   with    great   energy   and" 
liberation  of  nitrous  fumes.     Hydrochloric  acid  is  without 
action  on  the  metal.     Sulphuric  acid,  when  boiled  upon  it, 
dissolves  mercury,  while  sulphurous  anhydride  is  given  off; 
but  it  has  no  action  upon  it  in  the  cold. 

Mercury  is  used  in  medicine,  mixed,  by  simple  grinding 
with  chalk,  into  a  grey  powder ;  and  when  incorporated  with 
a  proper  proportion  of  conserve,  it  forms  what  is  well  known 
as  blue  pill.  It  acts  as  a  powerful  metallic  poison.  Work- 
men exposed  to  its  vapours  in  the  operations  of  gilding 
suffer  from  a  peculiar  tremulous  affection,  called  mercurial 
palsy ;  and  it  often  produces  salivation,  with  ulceration  of 


272  Compounds  of  Mercury. 

the  mouth  and  throat.  Some  of  its  salts,  such  as  corrosive 
sublimate,  when  swallowed,  act  as  immediate  and  powerful 
irritants,  producing  speedy  death. 

Mercury  is  largely  used  in  philosophical  enquiries.  Its 
expansion  in  glass  is  employed  as  a  measure  of  temperature 
in  the  thermometer ;  and  it  is  not  only  a  requisite  in  the 
construction  of  the  barometer,  but  it  furnishes  an  indispen- 
sable liquid  in  the  apparatus  used  for  the  accurate  collection 
and  measurement  of  gases. 

Mercury  forms  two  oxides :  the  grey  or  black  oxide 
(Hg2O),  and  the  red  oxide  (HgO)  :  both  of  them  yield 
salts  when  treated  with  acids. 

Mercurous  Oxide  (Hg2O)  is  a  powerful  base,  but  is  unstable 
when  isolated.  Exposure  to  light  or  to  a  moderate  heat  causes 
it  to  separate  into  the  metal  and  the  red  oxide,  Hg2O  becoming 
Hg  +  HgO.  It  is  best  obtained  by  grinding  calomel  with 
caustic  soda  in  excess,  and  washing  out  the  sodic  chloride — 

2HgCl  +   2NaHO     =     Hg20  +   2NaCl  +   H2O. 

Mercuric  Oxide,  or  the  red  oxide  (HgO),  is  obtained 
slowly,  in  red  scales,  by  heating  mercury  to  300°  or  400°  in 
an  open  flask  with  a  long  neck  for  some  days  ;  but  it  is 
more  conveniently  procured  by  heating  the  nitrate  cautiously 
till  it  is  converted  into  a  bright  scarlet  powder.  It  may  also 
be  precipitated  as  a  yellow  powder  by  adding  a  solution  of 
potash  or  soda  to  one  of  corrosive  sublimate. 

The  red  oxide,  when  heated,  becomes  black ;  and  at  a 
higher  temperature  is  separated  into  metallic  mercury  and 
oxygen,  It  is  easily  dissolved  by  acids. 

Mercury  forms  two  sulphides,  Hg2S  and  HgS,  the  latter, 
cinnabar,  constituting  the  principal  ore  of  the  metal.  It  is 
formed  artificially  by  subliming  mercury  with  about  a  sixth 
of  its  weight  of  sulphur,  when  it  furnishes  the  beautiful  red 
pigment  known  as  vermilion.  This  sulphide  is  also  obtained 
as  a  black  precipitate  by  decomposing  a  soluble  mercuric 
salt  with  sulphuretted  hydrogen  in  excess. 


Mercury  and  Chlorine.  273 

Mercury  also  forms  two  chlorides,  calomel  (HgCl)  and 
corrosive  sublimate  (HgCl2). 

Calomel,  or  Mercurous  Chloride  (HgCl),  is  a  heavy,  white, 
insoluble  powder,  which  may  be  obtained  by  mixing  a  solu- 
tion of  sodic  chloride  with  one  of  mercurous  nitrate ;  but  it 
is  more  commonly  obtained  by  converting  4  parts  of  mercury 
into  sulphate  by  boiling  it  to  dryness  with  6  parts  of  oil 
of  vitriol,  and  then  grinding  the  dry  mass  with  4  parts  more 
of  mercury  and  3  parts  of  sodic  chloride,  and  heating  the 
mixture.  Mercuric  sulphate  is  first  obtained — 

Hg  +   2H2SO4     =     HgSO4  +  2H2O  +  SO2. 
This  sulphate  is  then  converted,  by  the  additional  mercury, 
into  the  mercurous  sulphate — 

Hg  +  HgS04     =     Hg2S04; 

and  this,  by  sublimation  with  common  salt,  is   converted 
into  calomel  and  sodic  sulphate — 

2NaCl  +  Hg2SO4     =     2HgCl  +  Na2SO4. 

Exp.  255. — Heat  a  little  calomel  in  a  test-tube  :  it  will  sub- 
lime without  melting,  and  condense  on  the  cold  sides  of  the  tube. 

Exp.  256. — Place  a  small  quantity  of  calomel  at  the  bottom  of 
a  short  quill  tube,  cover  it  with  a  layer  of  dried  sodic  carbonate 
1 5  mm.  thick,  heat  the  sodic  carbonate  to  redness,  and  gradually 
sublime  the  calomel  through  it :  white  metallic  globules  of  the 
metal  will  condense  in  the  cold  part  of  the  tube. 

Corrosive  Sublimate,  or    Mercuric   Chloride   (HgCl2),   is 
usually  prepared  by  grinding  5  parts  of  mercuric  sulphate 
with  2  of  common  salt,  and  subliming  the  mixture — 
HgSO4  +   2NaCl     =     HgCl2  +   Na2SO4. 
Its  fumes  are  very  acrid  and  poisonous. 

Corrosive  sublimate  melts  easily ;  and  when  heated  further, 
boils  (at  295°),  furnishing  vapours,  which  condense  in  semi- 
transparent  or  in  white  crystals.  It  is  freely  soluble  in  water, 
alcohol,  and  ether.  It  is  the  most  important  of  the  soluble 
mercuric  compounds.  It  is  a  strong  antiseptic. 

Exp.  257. — Whip  up  the  white  of  an  egg  with  water;  strain  it 
T 


274  Tests  for  Mercury. 

through  muslin.  Add  a  little  solution  of  corrosive  sublimate  :  an 
immediate  coagulation  of  the  white  of  egg  will  occur.  Such 
coagulated  albumen  is  not  liable  to  putrefy. 

Wood,  cordage,  and  canvas  are  sometimes  soaked  in  a 
solution  of  the  salt,  and  are  thereby  rendered  less  likely  to 
decay. 

Mercuric  Iodide  (HgI2). — Add  to  a  dilute  solution  of 
potassic  iodide  a  few  drops  of  a  solution  of  corrosive  sub- 
limate :  a  yellow  precipitate  of  mercuric  iodide,  becoming 
salmon-coloured,  and  ultimately  brilliant  scarlet  (HgI2),  is 
formed.  This  iodide  is  redissolved  by  an  excess  of  potassic 
iodide,  or  by  one  of  corrosive  sublimate  :  with  the  iodide  it 
forms  a  soluble  double  salt  (KI,  HgI2),  and  a  similar  double 
salt  with  corrosive  sublimate  (HgI2,  2HgCl2). 

Exp.  258. — Heat  a  little  of  the  mercuric  iodide  in  a  dry  test- 
tube  :  it  will  melt  and  sublime,  and  condense  in  yellow  crystals. 
Shake  out  the  sublimate  upon  a  piece  of  paper,  and  draw  a  glass 
rod  firmly  across  the  heap  of  crystals :  a  scarlet  colour  will  be 
produced. 

This  change  is  brought  about  by  the  conversion  of  the 
yellow  rhombic  plates  into  a  dimorphous  red  octahedral  form 
by  the  molecular  disturbance  occasioned  by  pressure. 

Tests  for  Mercury. — All  the  salts  of  this  metal  are  vola- 
tilised by  heat-  They  are  all  reduced  to  the  metallic  state, 
whether  soluble  or  insoluble,  by  being  boiled  with  an  excess 
of  stannous  chloride.  If  a  slip  of  copper  be  boiled  in  a 
solution  of  a  salt  of  mercury,  it  becomes  coated  with  a  white 
amalgam  ;  and  if  the  copper  be  heated  in  a  small  tube  to 
redness,  globules  of  mercury  are  driven  off,  and  condense 
upon  the  sides.  Mercurous  salts  give  a  black  precipitate 
with  sulphuretted  hydrogen  ;  a  white,  consisting  of  calomel, 
with  a  soluble  chloride  j  and  this  white  precipitate  is  black- 
ened by  the  addition  of  ammonia,  but  is  not  redissolved  by 
it.  It  is  soluble  in  chlorine  water  or  in  boiling  nitric  acid. 
Mercuric  salts  give  a  yellow  precipitate  with  solution  of 
potash,  and  a  white  one  with  ammonia ;  with  sulphuretted 


Properties  of  Silver.  275 

hydrogen  a  white,  passing  through  brownish-red  into  black. 
Their  reactions  with  potassic  iodide  have  been  already 
noticed. 

(64)  2.  SILVER  :  Symb.  Ag ;  Atom.  Wt.  108. — This 
beautiful  metal  has  been  known  and  prized  from  the  earliest 
ages.  It  is  found  commonly  in  the  native  state,  and  almost 
invariably  accompanies  galena  in  small  quantity,  in  the  form 
of  sulphide.  Mercury  is  used  on  a  large  scale  for  dissolving 
metallic  silver,  and  separating  it  from  earthy  and  other  im- 
purities, but  the  metallurgic  processes  by  which  silver  is 
extracted  are  somewhat  elaborate,  and  are  described  in  the 
text  book  on  *  Metallurgy.' 

Silver  has  a  white  colour,  with  a  tinge  of  red.  It  pos- 
sesses considerable  tenacity  and  malleability,  so  that  it  may 
be  drawn  into  very  thin  wire,  and  hammered  into  leaf.  It 
is  softer  and  more  fusible  than  copper,  and  requires  a  tem- 
perature of  1023°  C.  for  its  fusion  :  though  it  is  scarcely 
volatile  in  ordinary  furnaces,  it  may  even  be  made  to  boil 
under  the  very  intense  heat  of  the  oxyhydrogen  jet.  As  a 
conductor  of  heat  and  electricity,  it  is  unsurpassed.  It  does 
not  become  oxidized  at  any  temperature ;  but  it  has  a  sin- 
gular power  of  absorbing  oxygen  when  in  a  state  of  fusion, 
and  giving  up  the  gas  suddenly  when  it  solidifies.  It  com- 
bines slowly  with  chlorine,  bromine,  and  iodine.  Its  attrac- 
tion for  sulphur  is  very  considerable ;  the  brown  tarnish  that 
silver  acquires  by  exposure  to  the  air  is  due  to  the  formation 
of  a  thin  film  of  argentic  sulphide,  in  consequence  of  the 
action  of  the  metal  on  the  traces  of  sulphuretted  hydrogen 
occasionally  present  in  the  air.  This  tarnish  may  be  removed 
by  rubbing  the  surface  with  a  solution  of  potassic  cyanide. 
Nitric  acid  is  the  best  solvent  for  silver  ;  but  it  may  also  be 
dissolved  by  boiling  sulphuric  acid,  with  escape  of  sulphurous 
anhydride. 

Silver  is  seldom  used  alone,  as  it  is  too  soft  to  resist 
wear  ;  but  when  alloyed  with  either  7^  or  10  per  cent. 


276  Experiments  on  Silver  Solutions. 

of  copper,  it  is  extensively  employed  in  coinage  and  in  the 
manufacture  of  plate.  When  a  thin  layer  of  silver  is  applied 
to  the  surface  of  copper  or  of  steel  articles,  it  furnishes  what 
are  called  '  plated  goods/  Mirrors  for  lighthouses  are  plated, 
as  from  its  high  lustre  silver  furnishes  the  best  reflecting  sur- 
face for  such  purposes. 

Exp.  259. — Dissolve  a  sixpenny-piece  in  nitric  acid.  The 
solution  has  a  bluish  colour,  owing  to  the  presence  of  the  copper 
which  is  always  added  before  coining,  for  the  purpose  of  harden- 
ing the  metal.  Dilute  the  solution  with  200  c.  c.  of  water ;  then 
add  a  solution  of  common  salt  so  long  as  it  forms  a  precipitate  : 
white  flakes  of  argentic  chloride  are  formed.  Stir  the  mixture 
briskly  with  a  glass  rod  :  the  precipitate  will  collect  into  clots — 

AgNO3   +   NaCl     =     NaNO3   +   AgCl. 

Filter  the  solution.  The  presence  of  copper  may  be  proved  in 
the  clear  liquor  by  adding  ammonia  in  excess  to  a  portion  of  the 
liquid  :  a  blue  solution  is  formed. 

Exp.  260. — Place  the  blade  of  a  knife  in  another  portion  of  the 
tiltrate:  it  will  become  coated  with  metallic  copper. 

Exp.  261. — Take  the  precipitated  argentic  chloride  obtained 
in  Exp.  259,  and  after  having  washed  it  well  on  a  filter,  place  it 
in  a  test-glass  with  a  little  water;  add  two  or  three  drops  of 
sulphuric  acid,  and  then  place  a  slip  of  zinc  in  contact  with  the 
chloride,  and  leave  it  for  twenty-four  hours.  The  chloride  will 
be  reduced  to  metallic  silver,  which  will  have  a  grey  porous 
aspect,  while  zinc  chloride  will  be  found  in  solution.  Lift  out 
the  piece  of  zinc  carefully ;  wash  the  silver  first  with  water  con- 
taining a  little  sulphuric  acid,  then  with  pure  water.  Dry  the 
residue.  Place  a  small  quantity  of  it  upon  an  anvil,  and  strike 
it  a  blow  with  a  hammer  :  a  burnished  metallic  surface  will  be 
produced.  Place  a  little  of  the  grey  powder  upon  charcoal,  and 
heat  it  in  the  flame  of  the  blowpipe  :  it  will  become  melted  into 
a  brilliant  malleable  bead.  Dissolve  another  portion  in  nitric 
acid :  red  fumes  of  nitrogen  peroxide  escape,  and  argentic  nitrate 
is  obtained  in  solution. 

Silver  belongs  to  the  class  of  monads  ;  it  forms  only  one 
oxide  of  practical  importance  (Ag2O).  It  may  be  obtained 
as  a  brown  hydrate  by  adding  caustic  potash  to  a  solution 


Compounds  of  Silver.  277 

of  argentic  nitrate.  An  excess  of  potash  does  not  redis- 
solve  it  ;  but  it  is  easily  dissolved  by  an  excess  of  ammonia. 
Other  oxides  (Ag4O  and  2Ag2O2)  are,  however,  known. 

The  most  important  soluble  salt  of  silver  is  the  nitrate 
(AgNO3),  which  crystallises  in  colourless  anhydrous  tables  ; 
it  melts  at  a  moderate  heat,  and  when  cast  into  small  round 
sticks  forms  the  '  lunar  caustic  '  of  the  surgeon.  This  salt  is 
readily  decomposed  by  the  action  of  organic  matter,  espe- 
cially when  exposed  to  light  ;  hence  it  is  used  for  the  pre- 
paration of  ink  for  marking  on  linen,  as  the  stain  cannot  be 
removed  by  washing  with  soap.  If  it  fall  upon  the  skin,  it 
blackens  it.  A  strong  solution  of  potassic  iodide,  or  of  the 
poisonous  potassic  cyanide,  will  remove  these  stains  from 
the  skin,  or  from  linen. 

The  sulphide  (Ag2S)  often  occurs  naturally,  mixed  with 
lead  sulphide  in  small  quantity.  It  may  also  be  precipitated 
as  a  black  hydrate  when  any  silver  salt,  soluble  or  insoluble, 
is  exposed  to  a  solution  of  sulphuretted  hydrogen. 

The  chloride  (AgCl)  is  white,  insoluble  in  water  and  in 
nitric  acid,  even  if  boiling,  but  freely  soluble  in  ammonia. 
If  heated  to  redness,  it  melts  into  a  horny-looking  mass.  The 
precipitated  chloride  becomes  of  a  dark  purple  colour  when 
exposed  to  the  light,  owing  to  the  formation  of  a  subchloride. 

The  bromide  (AgBr)  is  white,  insoluble  in  water  and  nitric 
acid,  and  sparingly  soluble  in  ammonia. 

The  iodide  (Agl)  is  of  a  pale  yellow,  and  is  nearly  in- 
soluble in  ammonia. 

The  chloride,  bromide,  and  iodide  of  silver  may  be  re- 
duced to  the  state  of  metallic  silver  by  fusing  them  in  a 
clay  crucible  with  half  their  weight  of  dry  sodic  carbonate, 
For  example  — 

4AgCl   +   2Na2CO3   =   4NaCl   +   2Ag2   +   2CO2  +   O2 


They  are  all  soluble  in  a  solution  of  sodic  hyposulphite,  and 
form  an  intensely  sweet  solution  with  it.  When  exposed  to 
light  in  the  presence  of  argentic  nitrate  and  some  organic 


2,78  Properties  of  Gold.    - 

matter,  they  undergo  chemical  changes  which  form  the  basis 
of  the  common  processes  of  photography. 

The  formation  of  the  chloride,  bromide,  and  iodide  of 
silver,  and  the  properties  above  described  of  these  com- 
pounds, furnish  ready  tests  for  the  presence  of  silver;  but 
the  phosphates,  chromates,  oxalates,  tartrates,  and  citrates 
all  form  insoluble  precipitates  with  salts  of  silver.  Copper 
placed  in  a  solution  of  silver  nitrate  or  sulphate  separates 
the  silver  in  crystalline  plates;  zinc  also  reduces  the  salt, 
as  does  also  a  stick  of  phosphorus ;  but  the  most  beautiful 
effect  is  produced  by  adding  a  few  drops  of  mercury  to  a 
solution  of  silver  nitrate  containing  5  or  6  per  cent,  of  the 
salt.  A  beautiful  crystallisation,  known  as  the  '  silver  tree/ 
will  be  formed  in  a  few  days. 

(65)  3.  GOLD  :  Symb.  Au ;  Atom.  Wt.  196-6.— This 
valuable  metal  has  been  known  from  the  earliest  times,  for 
it  is  found  in  small  quantity  in  almost  every  country,  and  it 
always  occurs  in  the  native  state  alloyed  with  silver,  gene- 
rally in  a  proportion  varying  from  4  to  12  per  cent.  Many 
rivers  contain  it  in  their  sands.  In  Australia  the  gold  is 
associated  with  quartz  and  slate,  and  in  California  it  is 
found  in  the  detritus  of  quartz  and  granite.  Gold  is  ex- 
tracted by  a  mechanical  process  of  washing,  and  afterwards 
dissolving  in  mercury  such  portions  of  the  gold  as  are  in  a 
very -finely  divided  state.  The  mercury  is  afterwards  dis- 
tilled off,  and  condensed  again  for  use. 

Pure  gold  is  of  a  rich  yellow  colour  and  high  lustre  ;  it  is 
nearly  as  soft  as  lead.  It  is  very  ductile,  and  is  the  most 
malleable  of  the  metals,  so  that  it  may  be  hammered  into 
leaves  11,200  of  which  would  not  be  thicker  than  i  milli- 
metre, or  280,000  would  not  exceed  an  inch  in  thickness. 
A  leaf  of  gold,  attached  to  a  pane  of  glass,  and  held  up 
between  the  eye  and  a  light,  will  allow  a  green  or  purple  light 
to  pass  through.  Gold  leaf  is  extensively  used  for  gilding 
on  wood,  papier  mache',  and  metal,  to  the  surface  of  which 
it  is  attached  by  means  of  an  adhesive  varnish. 


Compounds  of  Gold.  279 

Gold  fuses  at  about  1 100°  C.  It  is  scarcely  volatile  in  the 
furnace,  but  in  the  intense  heat  of  the  oxy hydrogen  jet  it 
may  be  dissipated  in  purple  vapours.  Sulphuric  acid  does 
not  attack  it;  neither  does  the  nitric  or  the  hydrochloric 
acid  separately,  but  a  mixture  of  the  two  liberates  chlorine, 
and  this  gradually  dissolves  it,  forming  a  yellow  solution. 

Exp.  262. — Place  a  little  gold  leaf  in  two  test-tubes ;  to  one 
add  nitric,  to  the  other  hydrochloric  acid.  Even  when  heated 
with  the  acid  the  gold  leaf  remains  unaffected.  Pour  the  con- 
tents of  one  tube  into  the  other  :  the  gold  will  disappear  with 
effervescence.  Evaporate  this  solution  in  a  small  porcelain 
capsule  till  the  acid  is  nearly  all  driven  off :  auric  chloride  will 
be  left. 

Exp.  263. — Dilute  the  solution  with  3  or  4  c.  c.  of  water.  To 
a  portion  of  this  liquid  add  a  solution  of  ferrous  sulphate :  a 
brown  precipitate  of  finely  divided  reduced  gold  is  obtained,  and 
ferric  chloride  is  formed — 

6FeSO4  +   2AuCl3     =     2(Fe^SO4)   +   Fe^Cl6   +   2Au. 

This  is  a  common  mode  of  separating  gold  from  its  solutions. 

Add  to  another  portion  of  the  auric  chloride  a  solution  of  sul- 
phurous acid  :  on  warming  the  mixture  gold  will  be  precipitated — 

2AuCl3  +  3HaO  +  3H2SO3     =    6HC1  +  3H2SO4  +  2Au. 
A  solution  of  oxalic  acid  will  have  a  similar  effect — 

2AuCl3   +   3HaQO4     =     2Au   +   6HC1  +   6COa, 
carbonic  acid  being  produced. 

All  these  liquids  look  purple  when  viewed  by  holding 
them  between  the  eye  and  the  light,  owing  to  the  trans- 
parency of  the  finely  divided  gold. 

Gold  in  its  pure  state  is  too  soft  to  be  used  for  the  pur- 
poses of  coin  or  plate.  It  is  hardened  by  alloying  it  with 
about  a  tenth  or  a  twelfth  of  its  weight  of  copper.  Gold  is 
usually  triad  in  combination ;  it  however  forms  two  oxides 
(Au2O  and  Au2O3),  but  they  are  seldom  prepared.  The  tri- 
chloride (AuCl3),  obtained  by  dissolving  gold  in  a  mixture  of 
nitric  and  hydrochloric  acids,  as  above  directed,  is  the  most 
important  compound  of  the  metal.  When  heated  gradually 


280  Platinum. 

to  about  175°,  it  loses  chlorine  and  furnishes  aurous  chloride 
(AuCl),  a  pale  yellow,  sparingly  soluble  compound  ;  and  by 
a  heat  below  redness  all  the  chlorine  is  expelled,  and  me- 
tallic gold  is  left.  A  solution  of  the  trichloride  is  easily 
decomposed  by  organic  matter.  It  stains  the  skin  and 
other  organic  substances,  such  as  white  silk,  of  a  purple 
colour.  Its  solution  is  reduced  to  the  metallic  state  by 
many  metals,  such  as  copper,  mercury,  iron,  and  zinc,  as 
well  as  by  phosphorus,  and  by  several  other  substances. 
Stannous  chloride,  if  added  to  its  solution  in  quantity  not 
sufficient  to  reduce  the  whole  of  the  gold,  gives  a  fine 
purple,  known  as  purple  of  Cassius  (Au2Sn3O6,  4H2O).  It  is 
used  for  colouring  the  ruby  glass  of  Bohemia. 

(66)  4.  PLATINUM  :  Symb.  Pt ;  Atom.  Wt.  197. — This  is 
a  hard,  tough,  white  metal,  a  good  deal  resembling  silver  in 
appearance,  with  which  in  earlier  times  it  appears  to  have 
been  confounded.  It  is  the  densest  substance  known,  except 
osmium  and  iridium,  which  accompany  it  in  its  ores,  and  are 
equally  dense.  It  may  be  drawn  into  very  fine  wire,  and 
rolled  into  thin  foil.  On  account  of  its  great  infusibility  and 
its  power  of  resisting  all  acids  except  a  mixture  of  the  nitric 
and  hydrochloric,  it  is  extremely  valuable  to  the  chemist,  as 
it  furnishes  him  with  crucibles  and  other  apparatus  in  which 
he  can  in  most  cases  where  accuracy  is  required  fuse  and 
heat  the  various  bodies  subjected  to  analysis.  It  is  also  used 
as  the  negative  metal  in  Grove's  voltaic  battery. 

Platinum  is  of  comparatively  rare  occurrence.  It  is  found 
in  metallic  grains,  sometimes  associated  with  gold,  silver, 
copper,  iron,  and  lead,  but  it  is  almost  always  accompanied  by 
certain  other  metals,  which  are  never  found  without  it,  viz. 
palladium,  osmium,  iridium,  rhodium,  and  ruthenium. 

On  account  of  the  extreme  infusibility  of  platinum,  it  re- 
quires a  peculiar  and  complicated  mode  of  treatment.  The 
ore  is  treated  first  with  nitric  acid,  to  dissolve  out  the  common 
metals  ;  then  washed,  and  treated  with  hydrochloric  acid, 


Compounds  of  Platinum.  281 

and  again  washed  ;  after  which  the  residue  is  digested  at  a 
very  high  temperature  in  4  parts  of  hydrochloric  acid,  to  which 
about  i  part  of  nitric  acid  is  added  little  by  little.  When 
nothing  more  is  dissolved,  the  acid  liquor  is  decanted,  and 
mixed  with  a  strong  solution  of  sal  ammoniac.  Most  of  the 
platinum  is  thus  precipitated  as  a  yellow  double  chloride  of 
ammonium  and  platinum  (2H4NC1,  PtCl4).  This  is  washed 
and  then  heated ;  the  whole  of  the  ammonia  and  chlorine 
are  expelled,  and  the  platinum  is  left  as  a  grey  porous  mass, 
commonly  known  as  spongy  platinum.  This  is  then  pressed, 
and  forged  at  a  high  heat  into  bars  or  plates,  which  are 
afterwards  hammered  into  dishes  or  vessels,  rolled  into 
sheets,  or  drawn  into  wire.  This  method  is  now,  however, 
gradually  being  displaced  by  a  mode  of  melting  the  ore  by 
means  of  the  oxyhydrogen  blowpipe. 

Platinum,  if  heated  alone,  does  not  combine  with  oxygen 
at  any  temperature,  but  it  becomes  slowly  oxidized  if  heated 
with  the  caustic  earths  or  alkalies.  It  alloys  readily  if  ignited 
with  lead,  tin,  bismuth,  antimony,  or  any  of  the  more  fusible 
metals,  which  would  melt  a  hole  in  a  platinum  crucible  if 
heated  in  it. 

Platinum  belongs  to  the  group  of  tetrad  metals.  It  forms 
two  oxides  (PtO  and  PtO2).  They  both  correspond  to  salts 
of  the  metal,  but  these  are  seldom  prepared.  Platinous  oxide 
(PtO)  is  soluble  in  a  solution  of  potash,  furnishing  a  dark 
olive-green  liquid  ;  and  the  alkalies  also  combine  with  and 
dissolve  platinic  oxide  (PtO2). 

There  are  two  chlorides.  Platinic  Chloride  (PtCl4)  is  the 
salt  obtained  by  dissolving  platinum  in  a  mixture  of  hydro- 
chloric and  nitric  acids,  and  evaporating  the  solution  to  dry- 
ness  at  100°  C.  It  is  an  orange-coloured  deliquescent  sub- 
stance. If  heated  for  some  time  to  about  23  5°  C.  it  loses 
half  its  chlorine,  and  becomes  converted  into  the  olive- 
coloured  insoluble  platinous  chloride  (PtCl2).  At  a  heat 
below  redness  the  whole  of  the  chlorine  is  driven  off,  and 
metallic  platinum  is  left.  Platinic  chloride  forms  double 
salts  with  the  chlorides  of  the  alkali  metals  ;  that  with  potas- 


282  Noble  Metals. 

sium  (2KC1,  PtCl4)  forms  yellow  octahedra,  insoluble  in 
alcohol,  and  nearly  so  in  cold  water.  The  ammonium  com- 
pound (2H4NC1,  PtCl4)  is  commonly  employed  to  separate 
platinum  from  its  solutions.  The  sodium  salt  (2NaCl,  PtCl4, 
6H2O)  is  soluble,  and  crystallises  in  long  red  needles.  All 
these  salts  are  decomposed  at  a  red  heat  :  metallic  platinum 
is  left,  and  by  washing  may  be  obtained  free  from  the  alkaline 
chlorides. 

Solutions  of  platinic  salts  are  not  reduced  by  ferrous  sul- 
phate, but  they  are  so  by  mercurous  nitrate,  which  precipitates 
finely  divided  metallic  platinum.  Oxalic  acid  does  not  re- 
duce them,  but  a  solution  of  a  formiate  will,  if  heated  with  a 
neutral  solution  of  platinum,  cause  the  metal  to  be  separated 
in  a  powder. 

5.  Palladium  is  a  white  metal,  nearly  as  infusible  as  pla- 
tinum.    It  forms  a  brown  solution  when  dissolved  in  nitric 
acid. 

6.  Rhodium  is  a  very  hard  white  metal,  very  difficult  of 
solution,  even  in  the  mixture  of  nitric  and  hydrochloric  acids, 
its  salts  are  of  a  beautiful  rose  colour. 

7.  Osmium  occurs  in  extremely  hard  scales  alloyed  with 
iridium  and  ruthenium.     When  heated  in  a  current  of  air,  it 
becomes  oxidized,  and  gives  off  a  remarkable  volatile  oxide 
(OsO4),  which  has  a  peculiar  pungent  smell,  and  is  freely 
soluble  in  water.     Osmium  is  the  least  fusible  of  the  metals 

8.  Iridium  accompanies  osmium  in  the  ore  of  platinum, 
and  is  sometimes  found  native  and  nearly  pure.     It  is  a 
white,  very  hard,  and  brittle  metal,  which  furnishes  three 
oxides.     They  pass  readily  one  into  the  other,  and  furnish 
salts  which  differ  in  tint  \   hence  the  name  Iridium,  from 
iris,  the  rainbow. 

9.  Ruthenium  is  a  very  hard  brittle  metal,  scarcely  fusible 
before  the  oxyhydrogen  blowpipe.     It  absorbs  oxygen  at  a 
red  heat,  and  yields  several  oxides. 

These  metals  last  mentioned  are  found,  in  small  quantities, 
accompanying  the  ore  of  platinum  ;  but  they  are  so  rare  as 
not  to  need  further  description. 


APPENDIX. 


Page  69 

This  tendency  of  gases  to  mix  may  be  shown  in  a  still  more  striking 
manner  by  the  following  highly  instructive  experiment.     Adapt  to  one 


Fig.  2 1  A. 


end  of  a  glass  tube,  about  1,000  mm. 
long  and  10  mm.  wide,  by  means  of  a 
well-fitting  cork,  a  short  circular  porous 
cell,  such  as  is  used  for  galvanic  bat- 
teries ;  cover  the  cork  with  a  layer  of 
sealing-wax.  Support  the  tube  in  an 
upright  position,  with  the  open  end 
dipping  under  water,  and  invert  a  glass 
bell  jar  over  the  porous  cell  (fig.  2 1  A). 
Now  pass  up  hydrogen  into  the  jar  : 
immediately  gas  will  escape  from  the 
open  end  of  the  tube  ;  the  hydrogen 
passing  more  rapidly  through  the  sides 
of  the  porous  cell  than  the  oxygen  and 
nitrogen  (air)  can  pass  out,  thus  forcing 
these  latter  out  of  the  tube.  So  soon 
as  the  bubbles  cease  to  escape  remove 
the  bell  jar  :  the  water  now  rises  in  the 
tube  owing  to  the  rapid  diffusion  of  the 
hydrogen  into  the  atmosphere. 

By  the  aid  of  this  apparatus  the  student  can  investigate  for  himself  the 
phenomena  of  diffusion  ;  he  will  find  that  whenever  the  porous  cell  is 
surrounded  by  a  gas  lighter  than  air,  bubbles  will  escape  from  the  tube  ; 
when  surrounded  by  a  denser  gas  the  water  will  rise  in  the  tube,  the  rise 
being  strictly  proportional  to  the  density  of  the  gas. 

Page  1 10 

Detection  of  Nitric  Acid  or  Nitrates. 

Exp.  93. — Add  to  a  fragment  of  a  nitrate  in  a  test-tube  a  few  scraps 
of  copper  and  pour  on  it  three  or  four  drops  of  sulphuric  acid.  Heat 
the  mixture  gently  ;  red  fumes  will  be  given  off,  and  may  be  distinguished 


284  Appendix. 

readily,  even  when  very  small  in  amouht,  by  looking  through  the  tube 
obliquely  over  a  sheet  of  white  paper. 

The  sulphuric  acid  decomposes  the  nitrate,  setting  nitric  acid  free  ; 
and  this  in  its  turn  is  decomposed  by  copper  with  formation  of  nitric 
oxide,  which  unites  with  the  oxygen  of  the  air  to  form  the  red  fumes  of 
nitrogen  peroxide. 

Exp.  94. — Dissolve  a  crystal  of  a  nitrate  in  a  little  water  in  a  test- 
tube  ;  now  add  carefully  an  equal  volume  of  concentrated  sulphuric  acid, 
cool  the  mixture  perfectly,  then  pour  in  a  cold  solution  of  ferrous  sul- 
phate so  as  to  form  a  layer  above  the  acid  mixture.  A  characteristic 
dark  brown  ring  will  be  formed  at  the  line  of  contact  of  the  liquids. 

In  this  case  the  sulphuric  acid  reacts  on  the  nitrate,  producing  nitric 
acid,  which  is  deoxidised  by  the  ferrous  sulphate,  nitric  oxide,  ferric 
sulphate  and  water  being  formed — 

HaSO4   +     KNO3      =     HNO3   +   KHSO4 
2HNO3   +   3HaSO4   +   6FeSO4    =     2NO    +    3Fe2sSO4  +   4OH2. 

The  brown  ring  is  a  solution  of  the  nitric  oxide  in  the  excess  of  fer- 
rous sulphate,  as  the  following  experiment  proves. 

Exp.  95. — Introduce  concentrated  solutions  of  about  five  grms. 
potassic  nitrate  and  25  grms.  of  ferrous  sulphate  into  a  flask  closed  by  i 
cork  through  which  a  bent  tube  and  tube  funnel  are  passed  (fig.  22). 
Pour  in  about  eight  grms.  of  sulphuric  acid  through  the  funnel  and  wan 
gently :  a  gas  is  evolved  (nitric  oxide)  which  forms  red  fumes  with 
oxygen  of  the  atmosphere.  Pass  the  gas  into  a  cold  solution  of  ferrou 
sulphate :  a  dark  brown  solution  is  obtained.  Afterwards  pass  the  ga 
through  a  warm  solution  of  ferrous  sulphate  :  the  nitric  oxide  does  no 
dissolve  in  this  case,  and,  if  protected  from  the  air,  the  solution  remain 
colourless,  thus  proving  the  necessity  of  employing  cold  solutions  whe: 
testing  for  nitric  acid. 

Page  114 

Water  decomposes  nitrogen  peroxide,  forming  nitrous  and  nitric  acids- 
NaO4  +    HaO     =     HNOa   +   HNO3. 

Nitric  Anhydride  (NaO5). — Owing  to  the  fact  that  this  body  decom- 
poses spontaneously  it  is  extremely  difficult  to  prepare.     It  has  1 
obtained  by  decomposing  silver  nitrate  with  chlorine — 

2AgNO3   +   Cl,     =     NZO5   +    2AgCl   +   O. 

Nitric  anhydride  is  a  white  crystalline  substance,  which  is  converte 
by  water  into  nitric  acid — 

NaO5   +    H.O     =     2HNO3. 


Appendix.  285 

Page  130 

The  formation  of  potassic  chlorate  by  the  action  of  chlorine  on  the  hot 
solution  of  potash  is  at  once  explained  by  the  fact  that  on  heating  a 
solution  of  potassic  hypochlorite  it  splits  up  into  potassic  chlorate  and 
potassic  chloride — 

3KC1O     =     KC1O3   +   2KC1. 

Page  139 

Anhydrous  hydrofluoric  acid  has  been  obtained  by  strongly  heating 
the  compound  (KF,  HF)  in  platinum  vessels,  when  it  breaks  up  into 
potassic  fluoride  and  hydrofluoric  acid.  The  latter  is  condensed  in  a 
well-cooled  receiver,  to  a  colourless,  transparent,  mobile  liquid,  which 
boils  at  19*40°,  and  does  not  attack  glass,  provided  all  moisture  be  ex- 
cluded. 

Page  146 

Whereas  bleaching  by  chlorine  is  generally  a  process  of  oxidation, 
bleaching  by  sulphurous  acid  is  always  a  process  of  reduction  :  chlorine 
decomposes  water,  setting  free  oxygen  ;  sulphurous  acid  in  the  presence 
of  a  body  prone  to  take  up  hydrogen  decomposes  water,  setting  free 
hydrogen,  itself  combining  with  the  oxygen — 

Cl,   +    H2O     =     O   +   2HC1. 
H2S03  +   H20     =  H2  +   H2S04. 

The  bleaching  is  therefore  in  both  cases  usually  the  result  of  a  secondary 
reaction. 

Page  149 

The  following  equations  represent  the  reactions  which  occur  in  the 
process — 

2FeSa   +    iiO     =  Fe2O3     +   48  Oa. 

SO2   +   2HNO3     =  H2SO4   -1-   2NO2. 

NO2  +   SOa  +   HaO      =  H2SO4  +     NO. 

NO   +   O     =  NO2. 

The  nitric  peroxide  in  contact  with  water  and  SO2  is  again  reduced  to 
nitric  oxide,  &c. 


QUESTIONS  FOR  EXAMINATION. 


THE  following  questions  have  been  framed  in  accordance 
with  the  Syllabus  issued  by  the  Science  and  Art  Department 
of  the  Committee  of  Council  on  Education,  under  the  head 
of i  Inorganic  Chemistry.  First  Stage  or  Elementary  Course 
— Second  Stage  or  Advanced  Course,'  pp.  90,  91. 

The  student  will  do  well  to  exercise  himself  from  time  to 
time  in  answering  these  questions  without  reference  to  the 
text ;  and  the  general  reader  will  find  his  knowledge  of 
Chemistry  become  much  improved  by  adopting  the  same 
course.  Should  he  not  be  able  to  answer  any  particular 
question,  he  will  have  to  refer  to  the  page  of  the  book  as  in- 
dicated in  the  right-hand  column,  but  he  is  recommended 
not  to  write  his  answer  immediately,  but  to  wait  until  he  has 
thoroughly  mastered  the  text.  The  answer  should  as  far  as 
possible  be  given  in  the  student's  own  language,  not  in  that 
of  the  book. 

Teachers  who  prepare  their  lectures  from  this  book  are 
recommended  to  set  their  pupils  a  number  of  these  questions 
the  day  after  each  lecture :  the  answers  are  to  be  written  in 
full,  and  marks  given  to  each  paper.  Those  pupils  only  who 
thus  acquire  a  certain  number  of  marks  should  be  allowed 


Questions  for  Examination.  287 

to  compete  for  the  prize  or  prizes  at  the  end  of  the  term 
or  half-year. 

The  Teacher  can  easily  frame  other  questions  on  the  text, 
and  he  is  recommended  to  exercise  his  class  in  the  use  of 
chemical  formulae  and  the  numerical  statements  connected 
therewith,  the  measurement  of  gaseous  volumes,  the  con- 
version of  Fahrenheit  into  Centigrade  degrees,  the  use  of  the 
metric  system,  &c. 

C.  T. 


PAGE 
QUEST. 

1.  Give  a  definition  of  Chemistry        ....         2 

2.  What  is  the  difference  between  a  simple  and  a  compound 

body?    .  .  .  .  .  .  -2-5 

3.  What  do  you  mean  by  the  words  analysis  and  synthesis  ?  .         3 

4.  State  some  of  the  different  modes  of  chemical  action          .         4 

5.  Write  out  the  symbols  of  the  non -metallic  elements  with 

their  combining  weights  .  .  .  •     5»  6 

6.  Do  the  same  for  the  metals  .  .  .  .     5,  6 

7.  Describe  the  difference  between  combining   weights   and 

volume  weights  ....  196-8 

8.  Explain  the  equation  CaCO3  +  2HC1  =  CaCl2  +  H2O  +  CO2 

and  write  out  the  combining  numbers  for  each  element, 

H  representing  one  gram  of  hydrogen    .  .  .8 

9.  What  is  the  length  in  inches  of  the  French  metre,  or  unit 

of  length,  the  decimetre  being  3 '9 3  7  inches  ?      .  .11 

10.  Using  the  same  figures  (but  adding  cyphers  where  neces- 

sary), write  out  the  value  in  inches  of  the  decimetre,  the 
centimetre,  and  the  millimetre.  Also  the  decametre, 
the  hectometre,  the  kilometre,  and  the  myriometre  .  9 

1 1 .  Wliat  is  the  weight  of  a  gram  in  grains  English  ?  and,  if  a 

gram  be  represented  by  I  'O,  how  do  you  write  a  deci- 
gram, a  centigram,  a  milligram,  a  hectogram,  a  kilo- 
gram, and  a  myriogram  ?  .  .  .  1 1 

12.  How  many  cubic  inches  does  the  litre  contain  ?     Also  how 

many  pints  ?         .  .  .  .  .  .10 


288  Questions  for  Examination. 

NO.  OF 

QUEST.  FAGB 

13.  Using  the  same  figures  that  express  cubic  inches  or  pints, 

give  the  decalitre,  the  hectolitre,  the  kilolitre,  and  the 
myriolitre.  Also  the  decilitre,  the  centilitre,  and  the 
millilitre  .  .  .  .  .  .10 

14.  What  is  the  weight  of  a  cubic  metre  of  water?        .  .11 

15.  The  formula  for  converting  degrees  on  Fahrenheit's  scale 

to  corresponding  degrees  on  the  Centigrade  scale  is 
f(F.°  — 32)  =  C.°  ;  and  for  converting  Centigrade  to 
Fahrenheit,  |C.°  +  32  =  F.°.  Convert  112°,  45°,  37°,and 
2i4°F.,  into  corresponding  degrees  on  the  Centigrade 
scale  .......  

16.  Convert  9°,  84°,  95°  C.  into  F.°  .  .  .  — 

17.  Convert —7°, -45°, -39°  F.  into  C.° 

18.  Convert  -17°,  -30°,  -8°  C.  into  F.°  .  .       — 

19.  Give  examples  of  the  three  states  of  matter  .  .12 

20.  Which  of  the  elements  has  never  been  melted,  and  what 

gases  have  never  been  liquefied  ?  .  .  .13 

21.  How   do   you   distinguish   between   mixture   and    combi- 

nation ?  .....  13,  14 

22.  Is  atmospheric  air  a  mixture,  or  a  chemical  compound  ?    15,  38 

23.  Write    down    the    symbol,    atomic   weight,    the    atomic 

volume,  the  specific  gravity,  the  relative  weight,  the 
molecular  weight,  and  the  molecular  volume  of  oxygen  .  19 

24.  Show  how  you  get  from  245  grams  of  potassic  chlorate,  96 

grams  of  oxygen  .  .  .  .  .21 

25.  How  many  grams  of  oxygen  are  there  in  1,000  grams,   or 

I  kilogram,  of  potassic  chlorate  ?  .  .  .       — 

26.  Explain  some  of  the  properties  of  oxygen  .  22-28 

27.  50  cubic  centimetres  of  a  gas  are  measured  at  10°  C.  ;  how 

much  will  it  measure  at  24°  C.  ?  .  .  .28 

28.  30  cubic  centimetres  of  a  gas  at  o°  C.  are  measured  at  730 

mm.  pressure  ;  what  is  its  volume  at  750  mm.  the  tem- 
perature being  the  same  ?  28,  29 

29.  I  measure  100  cubic  centimetres  of  a  gas  at  12°  C.  ;  the  gas 

is  heated  until  it  becomes  145  cubic  centimetres.  What 
is  the  temperature  of  the  gas  under  these  altered  con- 
ditions? .  .  .  .  .  .28 

36.     A  litre  of  gas  is  measured  at  20°  C.  and  730  mm.      What  is 

its  volume  at  the  standard  pressure  and  temperature  ?      28,  29 

31.     Correct  for  temperature  50  cubic  centimetres  of  gas  mea- 
sured at  5°  C.  .  .  .  .  .28 


Questions  for  Examination.  289 

NO.  OF 

QUEST.  PAGE 

32.  Correct  for  pressure  18  cubic  centimetres  of  a  gas  at  o°C. 

and  730  mm.  ....  28-29 

33.  What  is  the  difference  between  the  specific  gravity  and  the 

relative  weight  of  a  gas  ?  29-30 

34.  What  is  the  difference  between  an  acid  and  an  anhydride  ?        31 

35.  What  is  the  usual  test  for  an  acid  ? — for  an  alkali  ?  31 

36.  What  is  a  base?     .  .  .  .  .  31 

37.  State  the  difference  between  an  acid  ending  in  ous  and  one 

ending  in  ic,  and  between  a  salt  ending  in  ite  and  one 
ending  in  ate  .  .  .  .  .32 

38.  Explain  this  equation  :  H2SO4  +  2KHO  =  K2SO4  +  2H2O       32 

39.  State  the  difference  between  ferrous  oxide  and  ferric  oxide, 

ferrous  sulphate  and  ferric  sulphate        .  .  -33 

40.  What  is  ozone  supposed  to  be  ?     Name  a  test  for  it,  and 

describe  its  properties    ....  34~3^ 

41.  What  is  the  specific  gravity,  relative  weight,  and  molecular 

weight  and  volume  of  nitrogen  ?  .  .  36 

42.  How  is  nitrogen  prepared  ?  and  describe  its  leading  pro- 

perties .  .  .  .  .  -3^ 

43.  When  limewater  turns  milky  in  the  presence  of  atmospheric 

air,  what  does  that  show  ?          .  .  .  39 

44.  What  is  the  weight  of  a  litre  of  dry  air  at  the  standard 

temperature  and  pressure  ?  .  .  -39 

45.  What  are  the  accidental  ingredients  of  the  atmosphere  ?     .       40 

46.  What  is  the  symbol  of  water;  its  atomic  and  molecular 

weights ;  its  specific  gravity  at  4°  C.  ?  The  specific 
gravity  of  ice  and  steam  ?  The  relative  weights  of  water- 
gas  or  vapour,  and  its  atomic  and  molecular  volumes  ?  41,  44,  65 

47.  State  some  of  the  methods  by  which  water  is  decomposed 

and  hydrogen  collected,  and  what  becomes  of  the 
oxygen  .  .  4J~44 

48.  How  much  steam  does  a  litre  of  water  at  100°  C.  produce?      44 

49.  How  are  the  fixed  points  in  the  thermometer  determined, 

and  what  precautions  must  be  taken  with  respect  to  the 
boiling  point  ?  .  .  .  .  .  -45 

50.  Describe  some  of  the  physical  properties  of  water  .  .       45 

5 1 .  What  takes  place  during  the  cooling  of  water,  and  what  is 

meant  by  the  point  of  maximum  density  of  water  ?         .       47 

52.  What  is  the  freezing  point  of  water  on  the  C.  and  F.  scales? 

53.  What  is  meant  by  the  specific  gravity  of  a  solid — gold,  for 

example  ?  .  .  .  .  .  .47 

U 


29°  Questions  for  Examination. 

NO.  OF 

QUEST.  P*^K 

54.     How  is  pure  water  obtained  ?  .  -47 

55-     Name  some  of  the  impurities  that  occur  in  water,  and  how 

they  are  detected  ....  49~52 

56.     What  is  the  difference  between  hard  and  soft  water  ?  53 

How  do  you  distinguish  between  the  temporary  and  the 
permanent  hardness  of  water  ?    .  .  .  53~54 

58.     Describe  Clark's  soap  test  .  .  .  54 

$9.     What  is  meant  by  a  saturated  solution  ?     .  .  .56 

60.  In  the  formula  Na2CO3,  ioH2O,  what  is  the  ioH2O  called  ?       57 

61.  Describe  the  difference  between  an  efflorescent  and  a  de- 

liquescent salt ;  also  between  a  hydrated  and  an  anhy- 
drous salt  .  .  .  .  -57 

62.  Describe  the  processes  for  obtaining  hydrogen  as  represented 

in  the  following  equations  : 
3Fe  +  4H2O  =  Fe3O4  +  4H2;  H2SO4  +  Zn  =  ZnSO4  + H2  59,60 

63.  Describe  some  of  the  properties  of  hydrogen          .  60,  6 1 

64.  What  is  meant  by  collecting  a  gas  by  displacement  ?          .61 

65.  How  are  gases  dried  ?  .  .  .61 

66.  WThat  is  meant  by  the  mixed  gases  ?  .  .  .61 

67.  Describe  some  of  the  methods  of  showing  the  composition 

of  water    by   synthesis,    such    as    by   the   use   of   the 
Cavendish  apparatus,  fig.  17,  and  the  Eudiometer,  fig.  18.       65 

68.  Describe  the  oxy-hydrogen  blow-pipe         .  .  .67 

69.  Give  some  account  of  diffusion       .  .  .  .69 

70.  Why  is  hydrogen  selected  as  the  unit  or  standard  of  com- 

parison for  atomic  weights  and  combining  volumes  ?     70,  195 

71.  What  is  meant  by  a  gas  volume?  .  .  .  70,  197 

72.  The  Crith  being  the  weight  of  I  litre  of  hydrogen  at  o°  C. 

and  760  mm.  pressure,  what  is  the  weight  of  10  litres, 
and  also  of  a  cubic  metre  of  hydrogen  ?  . 

73.  What    is    the   relative   weight   of  oxygen   in   criths  ?    of 

chlorine  ?  of  hydrochloric  acid  ?  of  ammonia  ?  .  .       — 

74.  What  is  the  weight  in  criths  of  4  cubic  metres  of  hydriodic 

acid,  and  also  of  ammonia  ?       . 

75.  What  is  meant  by  a  monad,  a  dyad,  a  triad,  and  a  tetrad  ? 

and  give  examples          .  .  .  .  72 

76.  Explain  the  terms  univalent,  bivalent,  tervalent,  and  quad- 

rivalent elements.     Also  perissad  and  artiad  elements    .       72 

77.  What  is  a  hydride?  .  .  .  .  •       73 


Questions  for  Examination.  291 


78.  Write    down    the    symbol,    atomic   weight,    atomic    and 

molecular  volume,  specific  gravity,  and  relative  weight 

of  carbonic  anhydride    .  .  .  .  •       73 

79.  What  do  you  understand  by  the  term  carbonate  ?   .  -74 

80.  Explain  the  equation  CaCO3  +  2HC1  =  CaCl2  +  H2O  +  CO2       74 

81.  Describe  some  of  the  properties  of  carbonic  anhydride       .       75 

82.  How  do  you  collect  this  gas  by  displacement,  and  how 

does  the  process  differ  from  that  for  collecting  hydrogen  ?       76 

83.  Show  the  composition  of  carbonic  anhydride  by  synthesis   80-  8  1 

84.  How  is  carbonic  anhydride  disposed  of  in  the  atmosphere  ?       83 

85.  Describe  some  of  the  varieties  of  carbon  and  their  properties       84 

86.  What  is  meant  by  allotropy  ?  .  .  .92 

87.  How  is  carbonic  oxide  prepared  ?  .  .  .  93,  95 

88.  Write  in  double  columns  the  different  properties  of  car- 

bonic anhydride  and  carbonic  oxide,  such  as 

CO2  is  CO  is 

non-inflammable  inflammable 

and  so  on  .  .  73-84,  93-96 

89.  What  is  the  axis  of  a  crystal  ?  .  .  .98 

90.  What  are  the  systems  under  which  crystals  are  arranged  ? 

and  give  an  example  of  each       .  .  .  100-^103 

91.  Describe  the  terms  amorphous,  dimorphous,  and  isomor- 

phous     ......          103,  140 

92.  Explain  the  formation  of  nitric  acid  from  nitre  or  from 

sodic  nitrate       .  .  .  .  .  .105 

93.  Give  an  example  of  double  decomposition  .  .  .     106' 

94.  Describe  the  properties  of  nitric  acid          .  .  .107 

95.  What  is  the  difference  between  N2O5  and  HNO3  ?  .     109 

96.  Describe  the  process  for  obtaining  nitrous  oxide,  and  state 

some  of  its  properties     .  .  .  .  .no 

97.  Explain  3Cu  +  8HNO3  =  3  (Cu2NO3)  +  2NO  +  4H2O        .     112 

98.  What  is  nitric  oxide  a  good  test  for  ?  .  .  .112 

99.  What  is  the  acid  in  a  nitrite  ?  and  give  the  formula  for  it  1  13-1  14 

100.  Give  a  list  of  the  chemical  compounds  of  nitrogen  and 

oxygen,  and  state  why  atmospheric  air  is  not  included 

in  this  list  .  .  .  .  .  104,  38 

101.  What  is  meant  by  multiple  proportion  ?     .  .  .194 

102.  Write    down    the    symbol,    atomic   weight,    atomic    and 

molecular  \olume,  specific  gravity,  and  relative  weight 

of  ammoniacal  gas          .  .  .  .  .1*4 

U  2 


292  Questions  for  Examination, 

NO.  OF 

QUEST.  PAGH 

103.  Describe  the  process  for  collecting  and  drying  ammoniacal 

gas         .  .  .  .  .  .  115-116 

104.  Describe  some  of  the  properties  of  ammoniacal  gas  116-117 

105.  How  much  of  this  gas  does  box-wood  charcoal  absorb  ?     .     117 

1  06.     At  what  temperature  does  ammoniacal  gas  become  liquid  ? 

also  solid  ?  .  .  .  .  .  1  1  7 

107.  What  is  the  difference  between  liquid  ammonia  and  liquor 

ammoniae?  .  .  .  .  .  117 

1  08.  What  condensation  takes  place  when  nitrogen  and  hydrogen 

combine  to  form  ammoniacal  gas  ?          .  .  .119 

109.     Explain  the  following  equation  :  MnO2  +  2NaCl  +  2H2SO4 


120 

no.     AlsoMnO2  +  4HCl  =  MnCl2  +  2H2O  +  Cl2  .  .     121 

in.     Describe  some  of  the  leading  properties  of  chlorine,  and 

why  it  is  called  a  halogen  .  .  .          120,  121 

112.  What     are     the     other     halogens,    and    what     is     their 

atomicity?          .  .  .  .  .          120,  140 

113.  What  is  the  bleaching  action  of  chlorine  ?   .  .  .123 

114.  How  is  hydrochloric  acid  directly  formed,  and  what  is  its 

relative  weight  ?  .  .  .  .  .123 

115.  Explain  NaCl+H2SO4  =  HCl  +  NaHSO4  .     125 

u  6.     What  is  the  analytical  method  of  showing  that  H  and  Cl 

are  present  in  hydrochloric  acid  gas  ?     .  .  .125 

117.     What  tests  may  be  used  for  the  detection  of  hydrochloric 

acid  and  the  chlorides  ?.  .  .  .  .     128 

1  1  8.     Give  a  list  of  the  compounds  of  chlorine  and  oxygen  .      129 

119.  Show,  by  means  of  precipitation,  the  difference  between 

potassic  chlorate  and  potassic  chloride   .  .      130 

120.  How  is  bromine  obtained  ?  .  .  .  .     132 

121.  Compare  hydrobromic  with  hydrochloric  acid         .  73,  140 

122.  What  is  the  acid  in  argentic  nitrate?  and  what  takes  place 

when  its  solution  is  added  to  a  weak  solution  of  potassic 
bromide?  .  •  •  •  •  *34 

123.  Give  some  numerical  data  respecting  iodine  .  .134 

124.  When  a  solution  of  starch  is  added  to  one  of  potassic  iodide, 

the  characteristic  blue  colour  is  not  produced  :  why  is 
this?      .......      136 

125.  What  is  the  symbol,  atomic  and  molecular  weight,  mole- 

cular  volume,   specific   gravity,   and  relative  weight  of 
hydriodic  acid  ?  .  .  •  •  *37 


Questions,  for  Examination.  293 


NO.   OF 


TAGS 


QUEST. 

126.  Explain  the  equation  PI3  +  sH2O  =  HZPHO3  +  3!!!  .     137 

127.  Compare  hydriodic  acid  gas  with  HC1,  HBr,  and  HF  73,  140 

128.  What  are  the  properties  of  HI?     .  .  .  .138 

129.  What  are  the  symbols  of  iodic  and  periodic  acids?  .      138 

130.  Why  cannot  you  describe  the  properties  of  fluorine  ?  .     138 

131.  Explain  this  equation :  CaF2  +  HS2O4  =  CaSO2  +  2HF  .     139 

132.  What  is  the  most  remarkable  property  of  hydrofluoric  acid, 

and  how  may  it  be  exhibited?    .  .  .          139,  174 

133.  Explain  this  equation :    SiO2  +  4HF  =  SiF4  +  2H2O          .     139 

134.  What  is  meant  by  the  term  dimorphous?  and  give  an  ex- 

ample   .......     142 

135.  Describe  some  of  the  properties  of  sulphur,  and  state  its 

allotropic  modifications,  and  how  they  are  obtained     141-143 

136.  Are  roll  sulphur  and  flowers  of  sulphur  allotropic  modifica- 

tions?   .......     144 

137.  Give  some  of  the  leading  data  respecting  sulphurous  anhy- 

dride     .  .....     145 

138.  Explain  the  equation:  2H2SO4  +  Cu  -CuSO4  +  SO2  +  2H2O    145 

139.  Describe  some  of  the  properties  of  sulphurous  anhydride     145-7 

140.  Why  is  oil  of  vitriol  so  named,    and  why  is  Nordhausen 

sulphuric  acid  so  called  ?  147,  148 

141.  Describe  the  English  process  for  manufacturing  sulphuric 

acid  on  a  large  scale       .  .  .  .  .     149 

142.  What  is  the  function  of  nitric  oxide  in  the  manufacture  of 

sulphuric  acid  ?  .  .  .  .  .     149 

143      Name  some  of  the  properties  of  sulphuric  acid,  and  the 

test  for  detecting  it        .  .  .  .          150,  151 

144.  What  is  meant  by  the  term  dibasic  ?  .  .  .151 

145.  What  is  meant  by  monad  metals,  and  by  dyad  metals,  and 

by  what   mark   are   the   latter  distinguished   from  the 
former?  .  .  .  .  .  15  j 

146.  What  is  the  difference  between  a  hyposulphite  and  a  sul- 

phite?  and  explain  the  use  of  sodic  hyposulphite  in 
photography      .  .  .  .  .  .152 

147.  Explain  the  equation  Na2SO3  +  S  =  Na2S2O3         .  .     153 

148.  What  is  the  difference  between  a  sulphide,  a  sulphite,  and 

a  sulphate  ?  .  .  -.  .  .       

149.  Explain  the  process  for  obtaining  sulphurettted  hydrogen, 

and  describe  the  properties  of  this  gas,  and  of  its  aqueous 
solution  .....  £53~5 


294  Questions  for  Examination. 


QUEST. 

1 50.  What  metals  may  be  precipitated  by  means  of  sulphuretted 

hydrogen?          .  .  .  .  .  .156 

151.  Describe  the  properties  of  carbon  disulphide  .  .157 

152.  What  is  there  peculiar  about  the  atomic  and  molecular 

volume  of  phosphorus  ?  .  .  .          159,  162 

153.  State,  in  a  double  column,  the  chief  differences  between 

crystalline  and  amorphous  phosphorus  .  161-2 

154.  Give  the  formulae  for  the  chief  compounds  of  phosphorus 

and  oxygen         .  .  .  .  .  .163 

155.  What  are  the  three  forms  of  phosphoric  acid  ?        .  .     164 

156.  What  is  the  difference  between  a  phosphate  and  a  pyro- 

phosphate?         .  .  .  .  .  .165 

157.  What  is  a  monobasic,  a  tribasic,  and  a  tetrabasic  acid  ?      .     166 

158.  How  is  phosphuretted  hydrogen  prepared?  and  what  are 

its  properties  ?   .  .  .  .  .  166-7 

1 59.  Describe  some  of  the  crystallised  and  amorphous  forms  of 

silica      .......     168 

1 60.  How  is  pure  silica  obtained  ?          .  .  .  .169 

161.  What  do  you  mean  by  dialysis  ?     .  .  .  .170 

162.  Give  the  formulae  for  fire-clay  or  alumina  silicate,  ferrous 

silicate,  and  lead  silicate  .  .  .  .171 

163.  What  is  the  composition  of  different  kinds  of  glass  ?  .17*1 

164.  Explain  the  equation  : 

2CaF2  +  2H2SO4  +  SiO2  =  SiF4  +  2CaSO4  +  2H2O        .     173 

165.  How  does  boron  occur  in  nature  ?  .  .  .175 

1 66.  Under  what  forms  has  boron  been  obtained  ?          .  .176 

167.  Give  the  formulae  for  boracic  anhydride,  boracic  acid,  and 

borax     .  .  .  .  .  .  175 

1 68.  What  is  the  atomicity  of  boron  ?  .  .  .176 

169.  What  are  polymeric  bodies?  and  give  examples  .     177 

170.  How  is  olefiant  gas  prepared,  and  why  is  it  so  named  ?      .     178 

171.  What  is  marsh   gas?  and  give  its   atomic  and  molecular 

weights,  its  specific  gravity,  and  relative  weight  .     1 79 

172.  What  is  the  principle  of  the  Davy  lamp  ?  .  180-1 

173.  Describe  Bunsen's  burner  ....     182 

1 74.  Describe  the  blow-pipe,  and  distinguish  clearly  between 

the  reducing  flame  and  the  oxidising  flame          .  .184 

175.  What  are  the  chief  products  of  the  destructive  distillation 

of  coal?  .....  186-7 


Qtiestions  for  Examination.  295 

NO.  OK  PA^W 

QUEST.  PAG* 

176.  Give  the  formulae  for  potassic  ferrocyanide,  and  describe 

how  it  is  prepared          .  .  .  .  .188 

177.  What  is  the  difference  between  a  simple  and  a  compound 

radical  ?  .  .  .  .  .  .189 

178.  Which  is  the  radical  in  NaCl,  HNO?,  and  also  in  KCN, 

and  which  of  the  three  contains  a  nitrion,  and  what  is  it  ?     189 

1 79.  Explain  the  equation  :  KCy  +  H2SO4  =  HCy  +  KHSO4     .     189 

1 80.  Give  some  account  of  the  atomic  theory,  and  distinguish 

clearly  the  four  laws  of  chemical  combination     .  191-2 

181.  How  do  you  distinguish  between  the  terms  atomic  weight 

and  chemical  equivalent  ?  J93-4 

182.  What  is    meant  by   the   terms   atom,   molecule,    atomic 

volume,  and  molecular  volume  ?  .  .  195 

183.  How  are  the  atomic  weights  of  the  elements  determined?    195-8 

184.  What  are  the  general  characteristics  of  the  metals  ?  198-201 

185.  What  is  the  specific  gravity  of  sodium,  magnesium,  alumi- 

num,   antimony,    zinc,   tin,   iron,   copper,   silver,  lead, 
mercury,  gold,  and  platinum  ?  and  give  also  their  fusing 

points                 ......  199 

1 86.  What  is  the  difference  between  an  alloy  and  an  amalgam  ?  201,  202 

187.  What  is  meant  by  a  native  metal  ?              .             .             .  202 

1 88.  Name  the  metals  of  the  alkalies  and  their  atomicity            .  203 

189.  What  is  the  atomicity  of  the  iretals  of  the  alkaline  earths  ?  203 

190.  What  is  there  peculiar  about  the  atomicity  of  the  six  metals 

allied  to  iron  ?    .  .  .  .  .  .     204 

191.  Name  the  nine  noble  metals  ....     295 

192.  How  is  potassium  prepared  ?  205 

193.  Explain  the  term  basic  oxide          ....     206 

194.  Explain  K2CO3  +  CaO,H2O  =  2KHO  +  CaCO3     .  .     206 

195.  Describe  some  of  the  properties  of  potassic  carbonate         .     207 

196.  What  is  nitre  ?  and  state  some  of  its  properties  and  uses       208-9 

197.  What  is  sea-salt,  and  how  is  it  obtained  ?  .             .211 

198.  Describe  briefly  the  manufacture  of  soda  from  sea-salt,  and 

explain  the  terms  ball  soda,  black  ash,  and  soda  ash     211-13 

199.  How  do  you  distinguish  between  the  salts  of  potassium  and 

those  of  sodium  ?  .  .  .  .  .214 

200.  What  is  Nessler's  test  ?       .  .  .  .  .217 

201.  How  is  baryta  obtained  ?  and  describe  its  properties  .     217 

202.  How  is  baric  sulphate  converted  into  a  soluble  sulphide?  .     2l8 


296  Questions  for  Examination. 

NO.  OF 
QUEST. 

203.  Describe  the  tests  for  barium  salts  .  .  .219 

204.  Give  a  few  particulars  respecting  strontium  .  .219 

205.  How  is  lime  obtained,  and  what  is  meant  by  quick  lime 

and  slaked  lime  ?.....     220 

206.  What  is  plaster  of  Paris  ?  .  ..  .  .  .221 

207.  Describe  some  of  the  varieties  of  calcic  carbonate  .  .     222 

208.  Name  some  tests  for  calcium  salts  ....     223 

209.  How  is  aluminum  obtained,  and  what  are  its  chief  pro- 

perties ?  ......  223-4 

210.  What  is  a  lake,  and  what  is  a  mordant  1     .             .  .224-5 

211.  State  some  of  the  properties  of  hydrate  of  alumina  .     225 

212.  Explain  A12O3  +  3C  +  3C12  =  A12C16  +  3CO            .  .     225 

213.  Explain  the  constitution  of  the  alums          .             .  .226 

214.  What  is  the  formula  for  the  best  fire-clay  ?              .  .     227 

215.  What  is  £/.r««y  ?     ......     228 

216.  Describe  some  of  the  tests  for  aluminum  salts         .  .     229 

217.  Name  some  of  the  chief  salts  of  magnesium  with  their  for- 

mulae and  tests  .....  .230-1 

218.  How  is  zinc  obtained  from  its  ore  ?  .  .  .  232 

219.  Describe  some  of  the  properties  of  zinc       .  .  .  232 

220.  Give  some  account  of  the  salts  of  zinc         .  .  .  233 

221.  How  is  cadmium  distinguished  from  zinc  ?  .  .  234 

222.  Give  some  account  of  cobalt  and  its  oxides  .  .  235 

223.  How  are   compounds  of  cobalt  distinguished  before   the 

blow-pipe  ?......     236 

224.  What  is  the  chief  ore  of  nickel  ?     .             .             .  .     236 

225.  What  are  the  more  important  ores  of  iron  ?             .  .     237 

226.  How  is  iron  obtained  from  clay  iron-stone  ?            .  .     238 

227.  How  is  cast  iron  converted  into  wrought  iron  ?       .  .     239 

228.  What  is  steel,  and  how  do  you  distinguish  it  from  iron  ?  239-240 

229.  Describe  the  compounds  of  iron  and  oxygen           .  .241 

230.  How  do  you  distinguish  between  ferrous  and  ferric  salts  ?  .     243 

231.  How  are  the  chromates  prepared  on  a  large  scale  ?  .     245 

232.  Describe  some  of  the  peculiarities  of  the  manganates  .     247 

233.  How   is   potassic   permanganate   prepared  ?   and  give   an 

illustration  of  its  use       .....     248 

234.  Give  some  tests  for  manganese       ....     248 


Questions  for  Examination.  297 

N°-  °F  PAGE 

QUEST. 

235.  Name  some  of  the  alloys  of  tin  .  .  .250 

236.  How  are  stannous  chloride  and  stannic  chloride  prepared  ?  251-2 

237.  What  are  the  atomic  and  molecular  volumes,  and  the  rela- 

tive weight  of  arsenicum  ?  .  .  .  253 

238.  Describe  the  two  compounds  of  arsenicum  with  oxygen      .     255 

239.  Give   an   account   of  Keinsch's  test  for  arsenic ;    also  of 

Marsh's  .....  255-6 

240.  What  is  Na2HAsO4,  I2H2O?       .  .  .  .257 

241.  Give  the  molecular  and  atomic  weights,  the  specific  gravity, 

the  relative  weights,  and  molecular  volume  of  arseniu- 
retted  hydrogen  .  .  .  .  .257 

242.  What  is  the  action  of  a  solution  of  argentic  nitrate  on  this 

gas?       .  .  .  .  .  .  .257 

243.  How  is  antimony  obtained  ?  .....     258 

244.  Describe  the  chief  properties  of  antimony  .  .  .258 

245.  What  are  the  compounds  of  antimony  with  oxygen,  hydro- 

gen, sulphur,  and  chlorine?        ....     259 

246.  How  do  you  distinguish  in  Marsh's  test  between  antimony 

and  arsenic  ?      .  .  .  .  .  .     260 

247.  Describe  some  of  the  properties  of  bismuth  .  .     260 

248.  What  is  the  formula  for  the  basic  oxide  of  bismuth  ?  .260 

249.  What  is  the  most  important  soluble  salt  of  bismuth  ?  .     260 

250.  Why  do  bismuth  salts  in  solution  generally  become  milky 

when  diluted?   .  .  .  .  .  .261 

251.  Describe  briefly  the  Welsh  process  of  copper-smelting        .     262 

252.  Describe  the  more  important  properties  of  copper  .  262-3 

253.  How  is  cupric  oxide  obtained  ?  .  .  .     263 

254.  What  is  the  formula  for  blue  vitriol  ?  264 

255.  Describe  the  tests  for  copper          ....     264 

256.  How  is  lead  obtained  from  its  sulphide  ?    .  .  .     265 

257.  What  are  the  chief  properties  of  lead  ?        .  .  .     265 

258.  What  is  the  action  of  pure  water  on  lead  ?  .  .     266 

259.  What  is  litharge,  and  what  is  minium  ?  .  .267 

260.  Describe  some  of  the  salts  of  lead  ....     268 

261.  How  is  the  presence  of  lead  detected  in  water  ?      .  .     269 

262.  Give  some  of  the  numerical  constants  of  mercury,  such  as 

its  specific  gravity,  melting  and  boiling  points,  atomic 
weight,  &c.         .  .  .  .  .270 

263.  What  is  cinnabar,  and  how  is  quicksilver  obtained  from  it?     270 


298  Questions  for  Examination. 

NO.  OF 

QUEST.  ™« 

264.  How  may  mercury  be  purified  ?  .  .  270-1 

265.  What  is  the  action  of  acids  on  mercury?    .  .  .271 

266.  What  is  vermilion  ?  .  .  .  ,  .272 

267.  Describe  the  chlorides  of  mercury,  and  give  the  formulae    .     273 

268.  What  tests  are  employed  for  mercurous  and  mercuric  salts?     274 

269.  Write  down  some  of  the  leading  properties  of  silver  .     275 

270.  What  is  the  action  of  common  salt  on  argentic  nitrate  ? 

and  express  the  reaction  in  the  form  of  an  equation        .     276 

271.  How  are  the  argentic  chloride,  bromide,  and  iodide  re- 

duced to  metallic  silver  ?  .  .  .  .277 

272.  Describe  some  of  the  properties  of  gold     .  .  .278 

273.  What  acid  dissolves  gold,  and  how  does  it  act  ?  .  .     279 

274.  How  is  the  purple  of  Cassius  formed  ?  .  .     280 

275.  What  are  the  properties  of  platinum  ?        .  .  .     280 

276.  What  is  the  atomicity  of  platinum  ?  .        .  .  .281 

277.  Describe  a  few  of  the  salts  of  platinum       .  .  .     281 


INDEX. 


ACIDS,  30 
—  names  of,  33 

Analysis,  3 
Anhydrides,  74  note 

Adularia,  227 
After-damp  of  mines,  180 

Anhydrous  substances,  57 
Aniline,  186 

Aerate,  169 
Albite,  227 

Annealing  glass,  171 
Anthracite,  86 

Alkalies,  30 

Antimoniates,  259 

—  metals  of  the,  203,  205 

Antimonic      anhydride, 

—  tests  for,  in  combi- 

160 

nation,  214 

Antimonious     anhydride, 

Allotropy,  92 

160 

Alloys,  metallic,  201 

Antimoniuretted     hydro- 

Alum, 226 

gen,  1  60 

—  various  kinds  of,  226 

Antimony,  258 

—  properties  of,  226 

•  —  crude,    of   commerce, 

Alumina,  224 

258 

—  properties  of,  224,  225 
—  sulphate  of,  226 

—  oxides  of,  259 
—  sulphides  of,  259 

—  silicates  of,  171,  227 

—  chlorides  of,  259 

Aluminum,  223 

—  compounds  of,  260 

—  properties  of,  224 
—  tests  for  aluminum  salts, 

Antimony  sulphide,  156 
Antiseptic  powers  of  char- 

229 

coal,  91 

Aluminum  bronze,  224 

—  properties    of  sulphu- 

Amalgam, 202 

rous  anhydride,  146 

Amethyst,  168 

Aqua-fortis,  104 

Ammonia,  114,  160 

Aragonite,  222 

—  sources  of,  114 

Argentic  bromide,  134 

—  preparation  of,  115 

—  chlorate,  130 

—  properties  of  ammonia- 

—  chloride,  130 

cal  gas,  116 

Arsenic,  whence  obtained, 

—  absorption  of  ammonia, 

242 

117 

Arsenic    anhydride,    160, 

—  solution  of,  117,  118 

256,^257 

—  analysis  of,  119 

Arsenic,  white,  255 

—  solution  of,  in  water,2i6 

Arsenicum,  253 

—  Nessler's  test  for,  217, 

—  preparation  of,  253 

note 

—  properties  of,  254 

Ammonia  oxalate,  223 

—  alloy  of,  254 

Ammonic  carbonate,   hy- 

—  compounds  of,  255 

dric,  217 
Ammonic  magnesic  phos- 

— tests  for,  255 
Arsenious  anhydride,  160, 

phate,  165,  231 

254>.  255>  257 

Ammonium,  215 

Arseniuretted    hydrogen, 

—  hydrate,  216 

160,  257 

—  nitrate,  no 

Asbestos,  230 

—  sulphide  and  carbonate 

Atmospheric  air,  15 

of,  185 

—  not  an  element,  15 

Amorphous  bodies,  103 

—  experiments  on,  16 

Amorphous  phosphorus, 

—  a    mixture    of    several 

162 

gases,  38 

BLE 

Atmospheric  air— cont. 

—  less  abundant  compo- 
nents of,  38 

—  carbonic  acid  in  the  air, 
83  . 

Atomic  theory,  the,  190 
Atomic  weights,  7, 192-196 

—  table  of,  198 
Atoms,  191,  195 
Attraction,  chemical,  4 
Augite,  228,  230 
Azote,  36 

Azotised  substances,  38 


BALL  SODA,  or  black 
ash,  213 

Baric  carbonate,  219 
• —  chromate,  245 

—  sulphate,  147,  151,  152 

—  sulphite,  147 

—  sulphide,  156 
Barium,  141,  217 

—  salts  of,  218 

—  tests  for  salts  of,  219 
Baryta,  217 

Basalt,  227 
Bases,  31 

—  names  of,  33 
Bell-metal,  201,  250 
Beryl,  229 

Biphosphate  of  soda,  164 
Biscuit  ware,  228 
Bismuth,  260 

—  properties  of,  260 

—  alloy  of,  260 

—  oxides  of,  160,  260 

—  sulphide  of,  261 

—  trichloride  of,  261 

—  nitrate  of,  261 
Bismuthic  anhydride,  160 
Bisulphites,  146 
Bittern,  or  mother  liquor. 

of  sea  water,  133 
Black-lead,  85 
Bleaching    cotton    goods 

and  paper,  123 

—  powder,  or  chloride  of 
lime,  130,  note 

—  properties    of    sulphu 
rous  anhydride,  1 46 


300                                     Index. 

BLE                                              CHR                                            CUL 

Blende,  141,  232 

Carbonate  of  ammonium, 

Chromium  —  cont 

Blowpipe,  mouth,  183 
—  use  of  the,  184 

185. 
—  of  lime,  220 

—  oxides  of,  244 
—  salts  of,  245 

Blue  pill,  271 

Carbonates,  74,  83 

Cinnabar,  272 

Bohemian  glass,  280 
Boiling  point,  45 

Carbonic  acid,  39,  83 
Carbonic  anhydride,  73 

Clays,  224,  227 
—  varieties  of,  227 

Bones  of   animals,   prin- 
cipal earthy  component 
of,  1  60 

—  formation  of,  74 
—  properties  of,  75 
—  density  of,  76 

Coal  gas,  185 
—  manufacture  of,  185 
—  products  obtained  from 

Boracic  acid,  175,  176 
Boracic  anhydride,  175 

—  test  for,  77 
—  sources  of,  77,  78 

heating  coal,  185,  186 
—  purification  of,  186 

—  source  of,  175 

—  decomposition  of,  80 

—  odour  of,  186 

Borax,  175 

—  synthesis  of,  81 

Coal,  pit,  86 

—  where  found,  175 

—  carbonic   acid    in    the 

Coal  tar,  185 

—  uses  and  properties  of, 

atmosphere,  83 

—  dyes    procured    from, 

175,  176 

Carbonic  oxide,  93 

186 

Boron,  174 
—  properties  of,  174-176 
—  mode  of  obtaining,  174 

—  formation  and  prepara- 
tion of,  94,  95 
—  properties  of,  96 

Cobalt,  235 
—  oxides  of,  235 
—  tests  for  salts  of,  236 

—  crystals  of,  174 

Cast  iron,  238 

Cobalt  nitrate,  235 

—  compounds  of,  175 
—  oxide  of,  175 

—  grey  and  white,  239 
Cerite,  229 

Coke,  87 
—  preparation  of,  88 

—  combination  with  fluo- 

Cerium, 229 

—  gas,  185 

rine,  176 

Cetylene,  177 

Colcathar,  147 

Brass,  201 

Chalybeate  waters,  55 

Columbium,  253 

Bromide,  134 

Charcoal,  lamp-black,  90 

Combination,  chemical,  t 

—  of  silver,  277 

—  antiseptic    powers     of 

—  mixture    distinguished 

Bromine,  132 

charcoal,  91 

from,  13 

—  properties  of,  132 

—  preparation  of,  88 

Combustion,  24 

—  sources  of,  ij2 

—  as  a  fuel,  89 

—  matter  when  burnt  not 

—  formation  of,  133 

Charcoal,  animal,  or  ivory 

destroyed,  24,  25 

Bronze,  201,  250 

black,  90 

Compound  radicals,  the- 

'Bull-dog' slag,  171 
Bunsen's  burner,  182 

—  preparation  of,  90 
Chemical  formulas,  7 

ory  of,  189 
Compounds,  3 

Chemistry,  scope  and  aim 
of,  i 

Condy's  green   disinfect 
ing  fluid,  247 

/CADMIUM,  234 

China,  basis  of,  224,  228 

Copper,  261 

V_x     —  oxide  of,  234 

Chlorates,  131 

—  properties  of,  262 

Csesium,  214,  215 

Chloric  acid,  129 

—  smelting,  262 

Calamine,  232 

preparation  of,  131 

—  oxides  of,  263 

Calcedony,  168 

—  oxide,  129 

—  chloride  and  sulphides, 

Calcic  carbonate,  222 

Chloride  of  lead,  134 

264 

—  chloride,  221 

—  of  lime,  130,  note 

—  tests  for,  264 

—  fluoride,  138 

—  of  mercury,  134 

Corrosive  sublimate,  273 

—  phosphate,  160 

—  of  silver,  277 

Corundum,  224 

—  silicate,  171 

Chlorides,   123,   130,  167, 

Crucibles,  171 

—  sulphate,  152,  160,  221 

1  68 

Cryolite,      whence      ob- 

— sulphide,  156 

Chlorine,  120 

tained,  138 

Calcium,  141,  219 

—  mode  of  obtaining,  120 

Crystals,  classification  of, 

—  compounds  of,  219,  220 

—  solution  of,  121 

97 

—  tests  for  calcium  salts, 

—  properties  of,  122,  123 

—  symmetry  of,  97 

223 

—  compounds  of  chlorine 

—  axes  of,  98 

Calico    printing,    colours 
in,  224 
Calomel,  273 

and  oxygen,  129 
—  combination  of  sulphur 
with  chlorine,  158 

—  cleavage  of,  99 
—  Cubic  system  of,  99,100 
—  square    prismatic,     or 

Carbides,  93 

Chlorine  acids,  130 

pyramidal,  system,  100, 

Carbolic  acid,  186 

Chlorous  acid,  129 

IOI 

Carbon,  73,  84 

—  anhydride,  129 

—  rhombohedral,  or  hexu 

—  varieties  0^.84-90 

Choke  damp,  78 

gonal  system,  101 

—  properties  of,  92 

Chromate  of  bismuth,  246 

—  prismatic  system,  icz 

—  compounds  of,  177 

—  of  cadmium,  246 

—  oblique  system,  102 

Carbon  disulphide,  157 

Chromates,  the,  245,  246 

—  doubly  oblique  system. 

—  properties  of,  157 

Chromic  anhydride,  235 

103 

—  preparation  of,  158 

Chromium,  244 

Culm,  or  anthracite,  86 

Index,.                                     301 

CUP                                               GOL                                             HYD 

Cupreous  oxide,  263 
Cupric  chloride,  264 

FELSPAR,     or    adu- 
laria,  227 

Gold  —  cont. 
—  properties  of,  278,  279 

—  oxide,  263 

—  varieties  of,  227 

—  alloy  of,  279 

—  sulphate,  145 

Fermentation,      carbonic 

—  oxides  of,  279 

-  -  sulphide,  156,  264 

anhydride  formed    by, 

Granite,  227 

Cyanogen,  188 

77 

Graphite,  85 

—  preparation  of,  188 

—  mode  of  checking,  146 

Guano,     phosphorus     in, 

-  properties  of,  188 

Ferric  oxide,  33,  147,  241, 

160 

—  its    property   of  com- 

242 

Gun-metal,  201,  250 

bining  with  the  metals, 

Ferrous    carbonate,    237, 

Gunpowder,  209 

188,  189 

243 

Gypsum,  221 

and  with  hydrogen, 

—  chloride,  21,  243 

188,  189 

—  oxide,  33,  241 

—  salts,  243,  244 
—  sulphide,  243 

HEMATITE,      red, 
237 

DAVY'S  safety  lamp, 
180,  181 

Filter,    paper,     how     to 
make  a,  90 

—  brown,  237 
Haematite         anhydrate, 

Decomposition,  3 
Destructive  distillation,  89 
Dialysis,  170 

—  for  water,  91 
Fire-bricks,  171 
—  clay,  171 

brown,  242 
Halogens,  140 
—  compounds  of  the,  140 

Diamond,  84 

—  damp  of  mines,  179 

—  compared    with   each 

Didymium,  229 

Flame,  structure  and  pro- 

other, 140 

Dihydric  sodic  phosphate, 

perties  of,  181,  182 

Harrogate  water,  155 

164,  165 

—  the  blowpipe,  184 

Hartshorn,  114 

Dimorphous  bodies,   103, 

—  the  reducing  and  the 

Hornblende,  230 

142 

oxidising  flames,  184 

Hydrates,  57 

Dioxide  of  barium,  217 

Flint,  169 

Hydric  disodic  arseniate, 

Dipotassic    sulphate,    or 
normal  sulphate,  151 

Fluorides,  138 
Fluorine,  138 

—  disodic  phosphate,  165 

—  sulphide,  156 

—  compound  of,  with  hy- 

— nitrate,  105 

Disodic  hydric  phosphate, 

drogen,  140 

—  potassic    sulphate,    or 

formation  of,  164 

Fluor  spar,  138 

disulphate,  151 

—  sulphite,  146 

Foil,  of  metals,  201 

—  potassic  sulphide,  156 

Distillation,  134 
—  destructive,  89 

Freezing  point,  45 
Fur  inside  a  boiler,  53 

—  potassic  sulphite,  146 
Hydride    of  phosphorus, 

Disulphates,  151 

1  66 

Disulphide  of  iron,  242 
Dithionic  acid,  144 

/^ALENA,  141,  265 

Hydrides,  73 
Hydriodic  acid,  137,  140 

Dolomite,  230 
Ductility  of  metals,  201 
Dutch  liquid,  178 
Dyads,   or   bivalent    ele- 

VJ   Gas  coke,  185 
Gases,  12 
—  experiments  with,  20 
—  measurement  of,  29 

—  properties  of,  137 
Hydrobromic  acid,  140 
Hydrocarbons,  177 
Hydrochloric    acid,  '  120, 

ments,  72,  73 

Gaseous  compounds  of  the 

123,  140,  167,  175 

different  elements,   72, 

—  properties  of,  124 

T^ARTHENWARE, 

73 
German  silver,  201,  236 

—  analysis  of,  125 
—  solution  of,  126 

.!:>    basis  of,  224,  228, 

Geysers  of  Iceland,  silica 

Hydrocyanic    acid,     180, 

—  manufacture  of,  228 

dissolved  in  the,  170 

189 

Effervescent  waters,  55 

Glass,   action    of   hydro- 

— properties  of,  189 

Elements,  chemical,  6 

fluoric  acid  on,  139 

—  test  of,  189 

—  combination,  i 

—  manufacture    of,     170, 

—  sometimes       obtained 

—  mode  of  occurrence,  4 

171 

from  kernels  and  leaves, 

—  number  of,  4 
—  division  into  metals  and 

—  window  glass,  or  crown 
glass,  171 

190 
Hydrofluoric    acid,    138, 

non-metals,  5 

—  plate  glass,  172 

140 

—  list  of,  with  their  sym- 

— bottle  glass,  172 

—  its  action  on  glass,  138, 

bols  and  atomic  weights, 
6 

—  Bohemian  glass,  172 
—  flint  glass,  172 

Hydrogen,.  58 

Emerald,  129 
Emery,  224 
Epsom  salts,  230,  231 

—  properties  of,  172,  173 
—  annealing,  173 
Glaze  for  stoneware,  228 

—  mode  of  preparing,  59 
—  properties  of,  60,  61 
—  union  of  hydrogen  and 

Erbium,  229 

Glucinum,  229 

oxygen,  63 

Ethylsulphuric  acid,  178 

Gneiss!  227 

—  diffusion  of,  69 

Eudiometer,  the,  65               '     Gold,  278 

—  its  atomic  weight  and 

3°2 


Index. 


HYD                                             MET                                             NOT 

Hydrogen  -cont. 

Lead  —  cont.                                Metals  —  cont. 

combining  volume,  the 

—  uses  of,  266                            —  sulphides  of,  T.SJJ-I.S? 

unit  or  standard  of  com- 

— oxides  of,  266 

—  properties  of,  199,  200 

parison,  70 

—  compounds  of,  267,  269 

—  table  of  gravities  and 

—  union    with    chlorine, 

—  salts  of,  268 

fusing  points  of,  199 

oxygen,  or  nitrogen,  71 

—  tests  for,  269 

—  malleability  of,  201 

—  gaseous  compounds  of 
the  different  elements, 

Lead  carbonate,  268 
—  chloride,  268 

—  alloys,  201 
—  amalgams,  202 

72,  73 
—  salts  of,  106 

—  chromate,  268 
—  iodide,  268 

—  native  metals,  202 
—  classification    of,    202- 

—  compounds    of,     with 

—  nitrate,  268 

205 

phosphorus,  166 

—  silicate,  171 

Metaphosphates,  166 

Hydrosulphates,  155 
Hypochlorous  acid,  129 

—  sulphate,  152,  268 
—  sulphide,  268 

Metaphosphoric  acid,  166 
Metastannic  acid,  251 

Hypochlorous  anhydride, 

Lime,  220 

Metric  system,  10,  n 

129 

—  hydraulic,  221 

Mica,  228 

Hypophosphorous     acid, 

—  uses  of,  221 

Mineral  waters,  55 

1  66 

—  quicklime,  220 

Mines,     fire-damp      and 

Hyposulphites,  152 
Hyposulphurous  acid,  144 

—  milk  of  lime,  220 
Limestone  rocks,  220,  221 

after-damp  of,  179,  180 
Minium,  267 

Liquids,  12 

Mirrors    for    lighthouses, 

Litharge,  267 

276 

T  CELAND  SPAR,  222 
-L     Indium,  234 
lodic  acid,  138 

Litmus-paper,  31,  note 
Loam,  227 

Mispickel,  or  arsenic  sul 
phide  of  iron,  242 
Mixture  distinguished 

—  anhydride,  138 
Iodide  of  silver,  277 
Iodides,  135 

MAGNESIA,  230 
Magnesic  chloride, 

from  combination,  13 
MofFat  water,  155 
Molecular  weights,    102- 

—  tests  for  the,  135,  136 
Iodine,  134 

230 

—  pyrophosphate,  231 

196 
Molecules,  72,  195 

—  properties  of,  134,  135 
—  tests  for,  135 

—  sulphate,  231 
Magnesium  metals,  229 

Molybdenum,  252 
Monads,  or  univalent  ele- 

— source  of,  136 

Magnesium,  146,  229 

ments,  72,  73 

Iridium,  282 
Iron,  237 
—  varieties  of,  237 

—  properties  of,  229,  230 
—  oxide  of,  230 
—  tests    for    magnesium 

Monobasic  acids,  166 
Mordants,  in  dyeing,  225 
Mosaic  gold,  251 

—  ores  of,  238 

salts,  231 

Muriatic  acid,  126 

—  modes     of    obtaining, 

Manganese,  246 

238 

—  oxides  of,  246,  247 

—  slag,  238 

—  compounds  of,  247 

NAPHTHENE,  177 

—  cast  or  pig  iron,  238 
—  properties  of,  240 
—  oxides  of,  241 

—  tests  for,  247 
Manganous  oxide,  246 
Maremma,    boracic    acid 

Nickel,  236 
—  properties  of,  236 
—  alloy  of,  236 

—  tests  for,  243 

in  the,  175 

—  oxides  of,  236 

Ironstone,  clay,  237,  238, 

Marl,  227 

Nitrate  of  bismuth,  261 

243 
—  black-band,  238 

Marsh  gas,  179 
—  where  found,  179 

—  of  silver,  277 
Nitrates,  109 

Isomorphous  bodies,  103, 

—  properties  of,  179 

Nitre,  or  saltpetre,  208 

140 

Marsh's  test  for  arsenic, 

Nitric  acid,  104 

Ivory  black,  90 
—  preparation  of,  90 

255 
Mercurial  palsy,  271 
Mercuric  chloride,  273 

—  distillation  of,  105 
—  properties  of,  107 
—  action  of,   on    metals, 

KELP,  137 
Kissingen     water, 

—  cyanide,  188 
—  iodide,  273 
—  oxide,  272 

108,  109 
Nitric  anhydride,  109,  160 
—  oxide,  112 

133 

Mercurous  chloride,  273 

Nitrides,  38 

Kreuznach  water,  133 

—  chromate,  246 

Nitrites,  114 

—  oxide,  272 

Nitrogen,  36 

Mercury,  270 

—  methods  of  obtaining, 

LAMP-BLACK,  90 
Lanthanum,  229 

—  properties  of,  270,  271 
—  compounds  of,  272 

36 
Nitrous  acid,  113 

Laughing  gas,  in 

—  oxide  of,  272 

—  anhydride,  113,  160 

Lead,  265 

—  tests  for,  274 

—  oxide,  no 

properties  of,  265 

Metals  the,  198 

Notation,  chemical,  6 

Index. 


303 


OIL 

OIL  GAS,  177 
Olefiant  gas,  177 

—  production  of,  178 

—  properties  of,  178 

—  name  of,  178 
Oolite,  222 
Opal,  169 

Ores,  analysis  of,  154 
Orpiment,  254,  257 
Osmium,  282 
Oxidation,  24 
Oxides,  24 

—  of  carbon,  73 

—  of  chlorine,  129 

—  of  iron,  241 

—  of  nitrogen,  104 

—  of  phosphorus,  163 
Oxygen,  the  word,  19 

—  mode  of  preparing  21, 
22 

—  properties  of,  22,  23 

—  abundance  of,  26 


—  test  for,  27 
Oxygen-sulphur  acids,  144 
Oxyhydrogen  " 
Oxhydrogen  j« 

Ozone,  34 

—  test  for,  34 


Oxyhydrogen  flame,  181 
Oxhydrogen  jet,  the,  65 


PALLADIUM,  282 

-L     Pearl-ash,  207 
Pentathionic  acid,  144 
Perchloric  acid,  129 
Periodic  acid,  138 
Petalite,  227 
Petrifaction,  170 
Phosphoric  acid,  163,  167 

—  formation  of,  164 

—  different  forms  of,  164 
Phosphoric   anhydride, 

160,  163 

Phosphorous  group,  159 
Phosphorus,  159 

—  properties  of,  159,  161 

—  where    and    how    ob- 
tained, 1 60,  161 

—  white  and    red    forms 
of,  162 

—  distillation  of,  162 

—  safety  matches,  162 

—  oxides  of  phosphorus, 
163 

—  compounds  of,  with  hy- 
drogen, 1 66 

Phosphorous  acid,  166 

—  anhydride,  160 

—  iodide,  137 
Phosphuretted  hydrogen, 

1 60,  166 

—  properties  of,  166,  167 

—  formation  of,  167 

—  behaviour  of  in   chlo- 
rine, 167 


REI 

Photography,  use  of  sodic 
hyposulphite  in,  152 

—  fixing  a  picture,  153 
Pig  iron,  238 
Pitchblende,  237 
Plaster  of  Paris,  221 

'  Plated  goods,'  276 
Platinic  chloride,  281 
Platinum,  280 

—  properties  and  uses  of, 
280 

—  compounds  of,  281 
Plumbago,  85 
Polythionic  acids,  144 
Porcelain,  basis  of,  224,228 

—  manufacture  of,  228 
Porphyry,  227 
Portland  stone,  222 
Potash,  caustic,  206 

—  lye,  206 

—  of  commerce,  207 
Potassic  carbonate,  207 

—  chlorate,  130 

—  chloride,  130,  207 

—  chlorite,  131 

—  cyanide,  189,  190 

—  dihyric  arseniate,  257 

—  hydric  carbonate,  208 

—  hydrate,  206 

—  hypochlorite,  130 

—  nitrate,  208 

—  perchlorate,  131 

—  permanganate,  248 
Potassium,  203,  205 

—  mode  of  obtaining,  205 

—  oxides  and  hydrate  of, 
206 

—  salts  of,  207 
Precipitate,  54,  note 
Prism,  103,  note 
Protosulphide  of  iron,  242 
Prussic  acid,  188 
Prussian  blue,  components 

of,  188  ^ 

—  formation  of,  190 
Psilomelane,  247 
Pumice,  228 

'Purple  of  Cassius,    252, 

280 

Putty  powder,  251 
Pyrites,  iron,  242 
Pyrolusite,  247 
Pyrophosphates,  165 
Pyrophosphoric  acid,  166 


QUARTZ,    silica    in, 
168 

RAIN  WATER,  49 
Realgar,  257 

Red  lead,  or  minium,  267 
Reinsch's  test  for  arfenic, 
255 


SOD 

Respiration,  carbonic  an- 
hydride produced  by,  77 
Rhodium,  282 
Rhombic  phosphate,  164 
Rouge,  jewellers',  242 
Rubidium,  214,  215 
Ruby,  oriental,  224 
Ruthenium,  282 


SAFETY  LAMP,   Sir 
H.  Davy's,  180,  181 

—  matches,   manufacture 
of,  162 

Saline  waters,  55 
Saltpetre,  or  nitre,  208 
Salt,  bay,  211 

—  cake,  211,  212 

—  common,  210,  211 

—  rock,  211 

—  table,  211 
Salts,  31 

—  names  of,  32,  33 
Sapphire,  224 
Saxony  blue,  148 
Scheele's  green,  255 
Sea  water,  56 

—  salt,  120 
Selenic  acid,  159 
Selenious  acid,  159 
Selenium,  158 

—  properties  of,  158,  159 
Seleniuretted    hydrogen, 

*59 

Sesquichloride  of  iron,  243 
Sesquisulphide    of    anti- 
mony, 259 
Silica,  1 68 

—  properties  of,  168,  169 

—  solution  of,  170 

—  petrifaction,  170 
Silicates,  170 
Silicic  fluoride,  171 
Silicon,  1 68 

—  preparation    and    pro- 
perties of,  1 68,  174 

—  oxide  of,  1 68 

—  compounds  of,  173,  174 
Silver,  275 

—  properties  of,  275 

—  oxide  of,  276 

—  compounds  of,  277 

—  tests  for,  278 

'  Silver  tree/  278 
Smalt,  235 
Smelling-salts,  216 
Spathic  iron,  237 
Speculum  metal,  250 
Spring  water,  50 
Soda,    caustic,    or   sodic 
hydrate,  210 

—  manufacture  of,  21-3 

—  ash,  212,  213 

—  crystals,  313 


304                                      Index. 

SOD                                               TUF                                             ZIR 

Soda  water,  how  made,  76 
Sodic  carbonate,  212 

Sulphuretted  waters,  55 
Sulphuric  acid,  147 

Tungsten,  253 
Type-metal,  201,  258 

—  carbonate,  hydric,  214 

—  importance       ot       the 

—  chloride,  211 

manufacture  of,  147 

—  hydrate,  210 
—  hyposulphite,  152 

—  mode  of  preparing,  148 
—  manufacture    of,  on  a 

T  TRANIUM,  237 

—  iodide,  137 

large  scale,  149,  150 

—  manganate,  247 
—  phosphates,  164,  165 

—  salts  of,  151 
Sulphuric  anhydride,  for- 

VANADIUM, 253 
Ventilation  of  rooms. 

—  stannate,  251 

mation  of,  148 

79 

—  sulphate,  211 

Sulphurous  acid,  144,  145, 

Vermilion,  pigment,  272 

Sodium,  210 

146 

Vitriol,  blue,  264 

—  oxides  of,  210 

Sulphurous       anhydride, 

—  green,  147 

Solid  bodies,  12 

145,  243 

—  white,  233 

Stalactites,  222 

—  production  of,  145,  146 

—  oil  of,  147,  150 

Stalagmites,  223 

—  properties  of,  145 

Stannic  acid,  252 

—  acid  and  salts,  146 

—  chloride,  251 
—  oxide,  250 

Superphosphate  of  lime, 
161 

WATER,  4: 
—  decomposition 

—  sulphide,  156,  251 

Symbols,  chemical,  6 

of,  42 

Stannous  chloride,  250,  251 

—  freezing  and  boiling  of, 

—  oxide,  250 

45 

—  sulphide,  251 

HTANTALUM,  253 

—  distillation  of,  48 

Steel,  239 

X      Tartar  emetic,  258 

—  rain  water,  49 

Stone-blue,  235 
Stoneware,    manufacture 

Telluretted  hydrogen,  159 
Telluric  acid,  159 

—  presence  of  air  in,  49 
—  spring  water,  50 

of,  228 

Tellurium,  158 

—  impurities    in    natural 

Strontic  sulphate,  152,  219 
Strontium,  219 

—  properties  of,  158,  159 
Tellurous  acid,  159 

waters,  50-52 
—  hard  and  soft,  53 

Sublimation,  134 

Test-papers,  31,  note 

—  fur  inside  a  boiler,  53 

Subphosphate  of  soda,  164 

Tests,   in  chemistry.   31, 

—  soap  test  for,  54 

Sulphate  of  barium,  218 

note 

—  mineral  waters,  55 

Sulphates,  141 

Tetrabasic  acids,  166 

—  sea  water,  56 

Sulphide  of   ammonium, 

Tetrads,  or  quadrivalent 

—  saturation,  56 

185 
—  of  barium,  218 

elements,  73 
Tetrathionic  acid,  144 

—  crystallisation,  58 
—  efflorescent    and    deli- 

— of  silver,  277 

Thallium,  269 

quescent  salts,  57 

Sulphides,  143 
—  of  metals,  155-157 

—  properties  of,  269                   —  compounds  of,  57 
Thorinum,  252                             —  composition  of,  63,  64 

Sulphites,  146 
—  properties  of  the,  147 
Sulphur  group,  141 
Sulphur,  or  brimstone,  141 
—  sources  of,  141 

Tin,  249 

—  alloys  of,  250 
—  oxides  of,  250 
—  compounds  of,  25? 
—  tests  for,  252 

—  synthesis  of,  65 
—  the  eudiometer,  65 
Water  of  crystallisation,  57 
Water  cisterns,  lead,  266 
slate,  266 

—  properties  of,  141 

Tin  salts,  251 

Weights  and  measures,  9 

—  crystals  of,  142 

Tincal,  or  crude    Indian 

Witherite,  219 

—  distillation  of,  143 

borax,  175 

Wolfram,  253 

—  roll    sulphur   of  com- 

Tinfoil, 249 

Woulfe's  bottles,  118 

merce,  144 

Tinstone,  249 

Writing-ink,  224 

—  flowers  of,  144 

Titanium,  252 

—  compounds     of,    with 
oxygen,  14-1 
—  and  with  chlorine,  158 

Touch  paper,  209 
Travertine,  223 
Triads,  or  tervalent  ele- 

^/-TTRIUM, 229 

Sulphur  salts,  259 

ments,  72,  73 

Sulphurets,  143 

Tribasic  acids,  166 

7  INC,  232 

Sulphuretted     hydrogen, 
i53»  i59»  242 

'  —  phosphoric  acid,  165 
Tricalcic  phosphate,  161 

l^t    —  properties  of,  232 
—  alloys  of,  233 

—  preparation  of,  153,  154 
—  properties  of,  154 

Trifluorides,  176 
Trisodic  phosphate,   164, 

—  salts  of,  233 
—  oxide,  233 

—  compounds  with  metals, 
156 

165 
Trithionic  acid,  144 

—  sulphate,  733 
Zirconic  chloride,  174 

—  tests  of,  157                       i     lufa,  223 

Zirconium,  252  *••-.!. 

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